A cryptic chemical weather log kept by Tarawa Atoll’s stony coral in the tropical Pacific archipelago has been cracked, helping scientists explain a century of peaks and troughs in global warming—and inflaming fears that a speedup will follow the recent slowdown.

Added to a growing body of research, the newly published findings indicate that all it would take to trigger what could be an historically unparalleled period of rising global temperatures would be a shift in the winds. And that type of change in the intensity of Pacific trade winds appears to happen every 20 to 30 years or so.

The coral-based findings, published Monday in Nature Geoscience, provide new historical data supporting previous modeling results and observations that point to the long-term waxing and waning pattern of the trade winds in affecting worldwide temperatures.

For the past few decades, the Interdecadal Pacific Oscillation, as the influential cycle is known, has been in what’s called a negative phase, meaning trades winds have been strong.

The growing body of scientific evidence indicates that this negative phase has played a heavy role in driving an approximately 15-year old slowdown in worldwide surface warming. It suggests that a speedup in warming may follow the next switch to the oscillation’s positive phase, when trade winds weaken, and the effects of the natural cycle exacerbate those of unnaturally increasing levels of greenhouse gases in the atmosphere.

Diane Thompson, a postdoctoral fellow at the National Center for Atmospheric Research who led the study published Monday, said we’re in a surface warming slowdown right now because the Pacific trade winds are strong. But she says that apparent bout of good fortune won’t last forever.

“When winds weaken, which they inevitably will, warming will once again accelerate,” Thompson said. “The warming caused by greenhouse gases and the warming associated with this natural cycle will compound one another.”

Strong tropical Pacific trade winds serve as an air conditioner for the world, scientists are concluding. They mix warm equatorial surface water into greater depths, and help bring cooler waters to the surface. But, like the window-mounted AC unit that cools your living room during summer, all the while heating the air outside, the strong winds aren’t cooling the planet. They’re just moving heat-wielding energy to where it will bother us less.

And, just like that window-mounted unit, the strong trade winds will eventually break down. When the global air conditioner breaks down, modeling and past experience suggest that the process will start to operate in reverse.

In February, Australian and American researchers who compared ocean and climate modeling results with weather observations published findings in Nature Climate Change advancing earlier studies that explored the oscillation’s global influence. They found that the effects of strong Pacific trade winds during the past two decades were “sufficient to account” for the recent slowdown in global warming.

The slowdown refers to slower-than-expected rates at which temperatures measured on the land and at sea surfaces have been rising since the turn of the century. The amount of energy being trapped on Earth continues to rise at a quickening pace, because of the effects of the thickening cloud of greenhouse gas pollution in the atmosphere, but more of that energy than usual has been ending up in the oceans. That ocean heat—while hard for many of us to notice directly—has been driving record-breaking global temperatures, with 2014 on track to be the hottest on record, and to more vicious tropical storms.

The Australian and American researchers drew a similar comparison in their paper between strong trade winds and a slight cooling in global surface temperatures from 1940 to the 1970s.

On Monday, a team of American and British scientists led by Thompson reported on their chemical analysis of a sample core bored out of coral on the most populated atoll of Kiribati, a postcard-worthy Pacific Ocean country comprising many small islands. The sample was selected for the coral’s location, growing just outside the mouth of a west-facing lagoon.

The scientists measured changes over time in the amount of manganese in the skeletons produced by coral growing since the 1890s. The waters inside the lagoon are sheltered by a ring of land from the trade winds, which blow from the east. When trade winds are weak, the lagoon’s waters are churned more frequently by gusts blowing from the west. When those gusts blow in, they kick up sediment in the lagoon, releasing manganese into the water that corals can use in place of calcium to grow their skeletons.

The team also measured strontium in a coral sample taken from Jarvis Island, an uninhabited speck of land southwest of Kiribati, to gauge historical surface water temperatures. Strontium levels in coral skeletons are affected by ocean temperatures.

The scientists found that winds blowing a century ago had a similar relationship with global weather as the more recent links that have been discovered by other scientists.

“We know that winds flip-flop between periods of strong trade winds and periods of weak trade winds,” Thompson said. “Our study shows that these winds play a role in the rate of global temperature rise.”

Thompson’s team found evidence in its Kiribati coral core of weak trade winds early in the 20th century. Those winds coincided with a period, from 1910 to 1940, when global temperatures rose faster than could have been caused by greenhouse gas pollution alone, given the still-nascent state of mass industrialization.

The group also found evidence that trade winds were stronger and surface temperatures were cooler from 1940 to 1970, providing additional evidence of the relationship between the Pacific trade winds and the rates at which global temperatures have been changing.

“The paper confirms the idea that tropical Pacific trade winds play a major role in global climate variability,” Matthew England, a professor at the University of New South Wales who was not involved with the coral study, said.* He said its findings support those from other recent studies, including February’s Nature Climate Change paper, which was published by a team that England led.

“What’s very much new here is the attribution of the early 20th century warming to weakened Pacific trade winds,” England said.

The use of coral cores in the study was praised by Braddock Linsley, a professor at the Lamont-Doherty Earth Observatory of Columbia University who studies ancient climatic conditions by analyzing coral skeleton samples. He was not involved with the study.

Linsley said the new results were “exciting,” suggesting that the “poorly understood, rapid rise” in surface temperature from 1910 to 1940 was, in part, “related to changes in trade wind strength and heat release from the upper water column” of the Pacific Ocean.

“The mounting evidence is coalescing around the idea that decades of stronger trade winds coincide with decades of stalls or even slight cooling of global surface temperatures, as heat is apparently transferred from the atmosphere into the upper ocean,” Linsley said.

Winds over the Atlantic Ocean also appear to modulate global surface temperatures, albeit to a lesser extent than those over the Pacific Ocean. The science isn’t settled on just how much those Atlantic winds, and other potential forces, have contributed to the heaving nature of global warming. “We’re still at the beginning” of this field of research, Stefan Brönnimann, a University of Bern professor who investigates climate variability, said. He also wrote a ‘news and views’ article for Nature Geoscience assessing and describing the new research. “Pacific and Atlantic influences are not mutually exclusive.”

The new study’s findings were limited by the fact that just one coral core was analyzed to serve as a proxy wind gauge—a shortcoming that the researchers aim to address. “Measurements of manganese in coral skeletons are difficult and time consuming,” Thompson said. “Now that we know how important they can be, we will be making more.”

Evidence of rising temperatures deep in the Pacific Ocean, even as surface temperature rise has slowed, has come in part from measurements of the rise of expanding seas. As global temperatures continue to increase, the hastening rise of those seas as glaciers and ice sheets melt threatens the very existence of the small island nation, Kiribati, whose corals offered up these vital clues from the warming past—and of an even hotter future, shortly after the next change in the winds.

According to Bishop Marcelo Sorondo, the chancellor of the Vatican’s Pontifical Academy of Sciences, the Pope wants to have a direct influence on the vital 2015 UN climate conference in Paris, the culmination of decades of negotiations that will help determine the planet’s future.

“The idea is to convene a meeting with leaders of the main religions to make all people aware of the state of our climate and the tragedy of social exclusion,” Sorondo was quoted as saying in the Observer.

“Just as humanity confronted revolutionary change in the 19th century at the time of industrialisation, today we have changed the natural environment so much,” he told a London meeting of Cafod, the Catholic development agency.

“If current trends continue, the century will witness unprecedented climate change and destruction of the ecosystem with tragic consequences.”

It will not be easy for Francis to convince the world’s 1.2 billion Catholics on so divisive a subject. There remain plenty of climate change sceptics in the Vatican’s own ranks – including Cardinal George Pell, the Vatican’s treasurer, who once claimed “plants would love” a doubling of the amount of carbon dioxide in the atmosphere.

Francis has previously spelled his desire to appear at the UN general assembly in New York next year.

And he has now announced a plan to issue a rare “encyclical” to the Church about climate change. A lengthy message, it will be passed down through ranks of Catholicism via its far-flung bishops and priests.

Neil Thorns, head of advocacy at Cafod, told the Observer: “The anticipation around Pope Francis’s forthcoming encyclical is unprecedented. We have seen thousands of our supporters commit to making sure their MPs know climate change is affecting the poorest communities.”

The Pope last spoke out on climate change earlier this month, when countries assembled for the UN summit in Lima, Peru.

Then, nations agreed upon a draft document that will form the basis for talks in Paris next year.

Francis addressed his message to Manuel Pulgar-Vidal, the Peruvian environment minister, when he said the world can only slow climate change “if we act together and agree”. “The time to find global solutions is running out,” he said.

That upper boundary was first settled on four years ago at another round of talks in Cancun, Mexico. On the centigrade scale, it equals two degrees above the global average temperature at the beginning of the Industrial Revolution — the “2C target.”

But where did that target come from in the first place? And even if we manage to stay below it, will it really protect the planet from serious harm?

The target has a long, winding history that is rooted as much in politics and economics as in science. It first surfaced in the 1970s when William D. Nordhaus, an economist at Yale who was studying global warming, pointed out in his then-rough models of the economy that the damages to society really started to intensify at that level of warming.

The nations of the world agreed in 1992 to try to head off the worst damage, in an ambitious but vague treaty that called for action to prevent dangerous interference with the climate.

That raised the question of how much warming would be dangerous. In the mid-1990s, the German government picked up on the 2C finding as a way to breathe life into the treaty.

A decade of subsequent research added scientific support to the notion that 2C was a dangerous threshold. Experts realized, for example, that at some increase in global temperature, the immense Greenland ice sheet would begin an unstoppable melt, raising the sea by as much as 23 feet over an unknown period. Their early calculations suggested that calamity would be unlikely as long as global warming did not exceed about 1.9 degrees Celsius.

“Risking a loss of the whole Greenland ice sheet was considered a no-go area,” said Stefan Rahmstorf, head of earth system analysis at the Potsdam Institute for Climate Impact Research in Germany. “We are talking about really sinking a lot of coastal cities.”

As the economic and scientific arguments accumulated, the Germans managed to persuade other countries to adopt the 2C target, turning it into official European policy. The proposal was always controversial, with African countries and island states, in particular, arguing that it was too much warming and would condemn them to ruin. The island states cited the potential for a large rise of the sea, and African countries feared severe effects on food production, among other problems.

But as a practical matter, the 2C target seemed the most ambitious possible, since it would require virtually ending fossil fuel emissions within 30 to 40 years. At Cancun in 2010, climate delegates made 2C one of the organizing principles of negotiations.

The talks culminating in Paris next year are seen as perhaps the best chance ever to turn that pledge into meaningful emissions limits, in part because President Obama has gone far beyond his predecessors in committing the United States, the largest historical producer of greenhouse gases, to action. That, in turn, has lured China, the largest current producer, into making its first serious commitments.

Yet even as the 2C target has become a touchstone for the climate talks, scientific theory and real-world observations have begun to raise serious questions about whether the target is stringent enough.

For starters, the world has already warmed by almost one degree Celsius since the Industrial Revolution. That may sound modest, but as a global average, it is actually substantial. For any amount of global warming, the ocean, which covers 70 percent of the earth’s surface and absorbs considerable heat, will pull down the average. But the warming over land tends to be much greater, and the warming in some polar regions greater still.

The warming that has already occurred is causing enormous damage all over the planet, from dying forests to collapsing sea ice to savage heat waves to torrential rains. And scientists realize they may have underestimated the vulnerability of the ice sheets in Greenland and Antarctica.

Those ice sheets now appear to be in the early stages of breaking up. For instance, Greenland’s glaciers have lately been spitting icebergs into the sea at an accelerated pace, and scientific papers published this year warned that the melting in parts of Antarctica may already be unstoppable.

“The climate is now out of equilibrium with the ice sheets,” said Andrea Dutton, a geochemist at the University of Florida who studies global sea levels. “They are going to melt.”

That could ultimately mean 30 feet, or even more, of sea level rise, though scientists have no clear idea of how fast that could happen. They hope it would take thousands of years, but cannot rule out a faster rise that might overwhelm the ability of human society to adapt.

Given the consequences already evident, can the 2C target really be viewed as safe? Frightened by what they are seeing, some countries, especially the low-lying island states, have been pressing that question with fresh urgency lately.

So, even as the world’s climate policy diplomats work on a plan that incorporates the 2C goal, they have enlisted scientists in a major review of whether it is strict enough. Results are due this summer, and if the reviewers recommend a lower target, that could add a contentious dimension to the climate negotiations in Paris next year.

Barring a technological miracle, or a mobilization of society on a scale unprecedented in peacetime, it is not at all clear how a lower target could be met.

Some experts think a stricter target could even backfire. If 2C already seems hard to achieve, with the world on track for levels of warming far beyond that, setting a tighter limit might prompt political leaders to throw up their hands in frustration.

In practice, moreover, a tighter temperature limit would not alter the advice that scientists have been giving to politicians for decades about cutting emissions. Their recommendation is simple and blunt: Get going now.

“Dealing with this is a little bit like saving for retirement,” said Richard B. Alley, a climate scientist at Pennsylvania State University. “All delay is costly, but it helps whenever you start.”

Annual average temperatures have continued to rise for the region as a whole throughout the recent slowdown in the pace of warming globally, according to a new analysis of conditions above 60 degrees north latitude.

Over the past five years, temperatures in the autumn and early winter have been warmer all across the Arctic than they were for the same period during the last 20 years of the 20th century, leading an international team of researchers producing the report to conclude that these Arctic-wide conditions “are an indication that the early 21st century temperature increase in the Arctic is due to global warming rather than natural variability.”

The report, released Wednesday, is the eighth annual status check on climatic changes at the top of the world and the effects those changes are having on flora and fauna there.

The effort, supported by the National Oceanic and Atmospheric Administration (NOAA) and the Office of Naval Research, is an attempt to provide a year-to-year summary of conditions whose changes are affecting weather patterns at lower latitudes and are opening to commercial development an ocean that long has been isolated year round by a thick sheath of ice.

During the past 30 years, the region has grown warmer and greener. The long-term decline in the extent of summer sea ice is opening the Arctic Ocean to economic activities ranging from shipping and oil exploration to fishing, noted Craig McLean, acting assistant administrator for NOAA’s Office of Oceanic and Atmospheric Research, during a briefing on the report conducted during the American Geophysical Union’s fall meeting in San Francisco.

The opening of the Arctic Ocean as the climate has warmed also opens a long, remote stretch of US coastline that the Navy must protect and the Coast Guard must patrol as ship traffic across the top of the world increases.

During 2014, “we continue to see the impact of a persistent warming trend in the Arctic that began over 30 years ago,” said Jackie Richter-Menge, a researcher at the US Army Corps of Engineers Cold Regions Research and Engineering Laboratory in Hanover, N.H. “We also continue to see the influence of significant year-to-year regional variations.”

Overall, the Arctic has been warming twice as fast as the lower latitudes.

One manifestation of those variations: Temperatures for the January-to-March period varied widely by region. Although it was still cold, Svalbard Airport registered 8 degrees C (14 degrees F) above its 1981-to-2010 average for the period. In late January, Alaska posted temperatures as much as 10 degrees Celsius above normal. Meanwhile, eastern North America saw temperatures running some 5 degrees C below normal.

The region’s sea ice thickened and became more extensive by winter’s end, compared with the end of winter in 2013. But by the end of the melt season three months ago, the ice had retreated to the sixth-lowest extent since 1979, when satellites began to keep track of the ice on a regular basis.

As the ice retreats, it leaves more open water to absorb sunlight that the ocean can return to the atmosphere as heat as autumn and winter arrive. Indeed, sea-surface temperatures across the Arctic have been increasing, with the Chukchi Sea posting gains of nearly 1 degree F per decade. Here, too, regional differences appear. The Laptev Sea and the Bering Sea posted temperatures 7.2 degrees F above the 1981-2010 average, while the Barents Sea above Norway was close to its 1981-to-2010 average.

Researchers with NASA and the Cooperative Institute for Research in Environmental Sciences (CIRES) noted that during the past 15 years, the retreat of summer sea ice has led to a 5 percent increase in the amount of energy the Arctic Ocean has taken up.

Some researchers had suggested that warming over an increasingly exposed Arctic Ocean should have led to an increase in evaporation and hence increased cloudiness in the summer. As that happens, the clouds, instead of sea ice, could act as a break on warming and perhaps on sea-ice loss there by reflecting sunlight back into space

But after analyzing data on clouds, the solar radiation the Arctic Ocean absorbs, and sea ice, the data showed “no long-term trend in clouds during the summer,” said Jennifer Kay, a scientist at CIRES who focuses on Arctic climate. This runs counter to conditions over the rest of the world’s oceans, which are covered with clouds, she explained.

The amount of cloudiness over the ocean during the summer varies from one year to another as weather patterns vary. But “there is no long-term trend … that would allow this masking of the surface,” she said.

The warming ocean and more sunlight has increased plankton populations in the upper ocean, with blooms more likely to occur twice a year than in the past. Plankton sit at the bottom of the food chain that supports a variety of marine life. The largest increases in plankton this year occurred off the coast of Russia.

And while on land, tundra has been greening in general, given the longer growing season, tundra across Eurasia has been browning – a trend the new Arctic report attributes to generally cooling summertime temperatures there.

The report also includes an update on polar bears – numbers that are incomplete because two broad regions, in the Russian Arctic and along the eastern and northern coasts of Greenland, are hard for scientists to reach, according to Jeff York, senior director of conservation for Polar Bears International, based in Bozeman, Mont.

Reductions in summer sea ice between 1987 and 2011 cut the polar bear population in western Hudson’s Bay by a third, from 1,200 animals to 800. Along the norther coast of Alaska and east into Canada, the population centered along the southern Beaufort Sea fell by 40 percent between 2001 and 2010 to around 900 bears. Since then the population appears to have stabilized. Several regions in northern Canada have seen populations that have remained stable, while one region hosts an increasing population of polar bears.

Meanwhile, the Greenland ice sheet has seen little change in mass between 2013 and 2014, said Martin Jeffries, an arctic specialist with the Office of Naval Research in Arlington, Va., even as it saw extensive surface melting.

Given the pace of change and projections that warming will continue, it’s vital to maintain and expand the tools in the region needed to monitor the changes, scientists say.

“If we’re to understand how this complex environmental system works, if we’re going to improve predictions of what’s likely to happen … and identify appropriate responses to the changes, we really need to add to our Arctic observing capabilities,” said Dr. Jeffries, the report’s principal editor.

The draft, now circulating among negotiators at a global climate summit meeting here, represents a fundamental breakthrough in the impasse that has plagued the United Nations for two decades as it has tried to forge a new treaty to counter global warming.

But the key to the political success of the draft — and its main shortcoming, negotiators concede — is that it does not bind nations to a single, global benchmark for emissions reductions.

Instead, the draft puts forward lower, more achievable, policy goals. Under the terms of the draft, every country will publicly commit to enacting its own plans to reduce emissions — with governments choosing their own targets, guided by their domestic politics, rather than by the amounts that scientists say are necessary.

The idea is to reach a global deal to be signed by world leaders in Paris next year, incorporating 196 separate emissions pledges.

“It’s a breakthrough, because it gives meaning to the idea that every country will make cuts,” said Yvo de Boer, the former executive secretary of the United Nations Convention on Climate Change.

“But the great hopes for the process are also gone,” he added. “Many people are resigned,” he said, to the likelihood that even a historic new deal would not reduce greenhouse gas levels enough to keep the planet’s atmospheric temperature from rising 3.6 degrees Fahrenheit.

That is the point at which, scientists say, it will become impossible to avoid the dangerous and costly early effects of climate change — such as melting glaciers, rising sea levels, extreme drought, food shortages and more violent storms.

The Lima draft represents the input of all the negotiating countries, though there are still several major hurdles to work out. But even then, experts say, at best the new deal might be enough only to curb global warming by about half as much as scientists say is necessary.

Until recently, the United States and China, the world’s two largest greenhouse gas polluters, have been at the center of the impasse over a climate deal.

Until this year, the United States had never arrived at the United Nations’ annual climate negotiations with a domestic policy to cut its own carbon emissions. Instead, it merely demanded that other nations cut their use of coal and gasoline, while promising that it would do so in the future.

China, meanwhile, was the lead voice among nations demanding that developing economies should not be required to commit to any cuts.

But in November, President Obama and President Xi Jinping of China announced plans to reduce emissions, helping inject new life into the global climate talks.

Negotiators here call the joint announcement between China and the United States the catalyst for the new draft, which, if approved at the climate summit meeting this week, would set the stage for a final deal to be signed by world leaders next year in Paris.

In the United Nations’ first effort to enact a climate change treaty, the 1997 Kyoto Protocol, the legally binding language of the agreement prescribed that the world’s largest economies make ambitious, specific emissions cuts — but it exempted developing nations. The United States Senate refused to ratify the treaty, effectively leaving it a failure.

The Lima draft does not include Kyoto-style, top-down mandates that countries cut emissions by specific levels. Instead, it includes provisions requiring that all nations, rich and poor, commit to policies to mitigate their emissions. Countries that sign on to the deal will commit to announcing, by March, detailed, hard-numbers plans laying out how they will cut emissions after 2020.

The draft that emerges this week “will look like a game of Mad Libs,” said one negotiator who was not authorized to speak publicly. Over the coming months, as countries put forth their emissions reduction pledges, the details of the final deal will be filled in.

It is expected that many countries will miss that March deadline. Officials from India and other countries have said that they are unlikely to present a plan before June.

In order to ensure that all countries are included in the deal, late announcers will get a pass. The point, United Nations officials say, is to ensure that the information exists to finalize a Paris deal by December 2015.

Negotiators concede that the “each according to their abilities” approach is less than perfect — but that it represents what is achievable.

“The reality of it is that nobody was able to come up with a different way of going about it that would actually get countries to participate and be in the agreement,” said Todd D. Stern, the lead American climate change negotiator. “You could write a paper, in theory, assigning a certain amount of emissions cuts to every country. That would get the reduction you need. But you wouldn’t get an agreement. We live in the real world. It’s not going to be perfect.”

And there are still many hurdles ahead.

While many major developing economies are now expected to follow China’s lead in preparing emissions plans, some countries remain wild cards. This year, the government of Australia repealed a landmark climate change law that taxed carbon pollution. Since then, its emissions have soared.

“Australia is left without any viable policy to cut emissions,” said Senator Christine Milne, the leader of the Australian opposition Green Party. “It’s going to drag its heels.”

Money, as always, is a sticking point.

The increasing likelihood that the planet’s atmosphere will warm past the 3.6 degree threshold, with or without a deal in Paris, is driving demands by vulnerable nations — particularly island states and African countries — that the industrialized world open up its wallet to pay for the damage incurred by its fossil fuel consumption. Under the terms of a 2009 climate change accord reached in Copenhagen, rich countries have agreed to mobilize $100 billion annually by 2020 to help poor countries adapt to the ravages of climate change. But a report this month by the United Nations Environmental Program estimates that the cost to poor countries of adapting to climate change could rise to as high as $300 billion annually — and vulnerable countries are stepping up their demands that more money be included in any final deal. Many vulnerable and developing countries insist that each country’s national pledge include not just a plan to cut emissions, but also money for adaptation.

“The financing question will be one of the deepest divides,” said Jennifer Morgan, an expert in climate change negotiations with the World Resources Institute, a research organization.

Another element to be hashed out by negotiators will be devising an international number-crunching system to monitor, verify and compare countries’ pledged emissions cuts.

China has always balked at any outside monitoring of its major economic sectors, and is pushing back on proposals for rigorous outside scrutiny.

Hong Lei, a spokesman for the Chinese Ministry of Foreign Affairs, said that his country “always supports increasing transparency” but that the new reporting system should reflect “the reality that developing countries’ basic capacities in areas like national statistics and assessment are still insufficient.” He added that “developed countries should provide appropriate support to developing countries.”

The United States has urged that a final deal not take the form of a legally binding treaty requiring Senate ratification, hoping to avoid a repeat of the 1997 Kyoto Protocol experience.

But many countries continue to press for a legally binding deal.

French officials have already given the yet-to-be-signed deal a working title: the “Paris Alliance.”

The name, they say, is meant to signify that many different economies are working together, rather than complying with a single, top-down mandate.

In the debate over how to address climate change, there is a glaring gap between the levels of carbon reductions the world must achieve to avert the worst consequences of global warming and the levels of reductions that national governments have been willing to make thus far. Bridging that gap will require cities and businesses — the chief drivers of carbon emissions — to play a leading role, and Lima’s experience points the way forward.

Lima recently secured an enhanced credit rating with the help of technical assistance from the World Bank and other agencies. That may not sound like a major advance, but consider: Without the credit rating, borrowing to invest in mass transit was too expensive for Lima’s government. With the credit rating, the city raised $130 million to upgrade its bus rapid transit system. That will significantly reduce carbon pollution from one of the most extensive transportation systems in the world, while also helping to reduce traffic congestion, which saves companies money and improves productivity.

Investing in modern, low-carbon infrastructure is one of the best ways to reduce emissions while also spurring economic growth. Such investments hold enormous benefits for urban residents and businesses, but local governments are often unable to make them because they lack access to the credit markets.

Climate Change

The World Bank estimates that only 4 percent of the 500 largest cities in developing countries have internationally recognized credit ratings, and only 20 percent have a domestic rating, leaving them with little ability to finance infrastructure improvements. Lima is one of the few cities in the region to obtain an enhanced credit status, but there are hundreds of cities all over the world that would benefit from this same step.

Providing cities with access to capital markets is unusually cost-effective. The $130 million that Lima raised was possible because the World Bank spent $750,000 providing the necessary technical assistance. In the field of global development, where resources are scarce, enhancing credit ratings offers attractive opportunities for countries and aid organizations alike.

Lima should be just the beginning. In the developing world alone, cities have about $700 billion in annual demand for sustainable infrastructure projects — such as transportation, energy, waste treatment and water supply. Providing them with access to credit could become one of the most effective ways to fight climate change, drive economic growth and — by reducing pollution — improve public health.

About 70 percent of carbon emissions come from cities, and a recent report found that if the world’s cities took bold yet achievable actions to reduce their emissions, the collective impact would be equal to halving global coal use over the next 40 years. With greater access to credit, those reductions would be far steeper.

Negotiators at the Lima conference should ensure that access to credit is squarely on the agenda. If more national governments empower cities to participate in capital markets, they will strengthen their economic engines while increasing their ability to set and achieve ambitious carbon reduction targets. There are few steps that offer such potential for progress at so low a cost.

There are also steps nations can take to unleash private sector investment in modern, low-carbon infrastructure — and they need not involve subsidies. In much of the world, renewable energy sources are already more affordable than fossil fuels, a trend that is likely to continue as technology advances and production costs fall.

Consider Peru’s southern neighbor, Chile. It is home to several solar companies that are building more than a gigawatt of new energy generation projects, which power cities and major industries, including the country’s large copper mines. Solar — long considered a niche energy source — will form the backbone of the nation’s low carbon power grid. This development was occurring before Chile enacted a modest carbon tax this year, which will spur even greater investment in renewable energy.

The changing market for renewables is creating opportunities for other nations to follow a similar path. A recent study by Bloomberg New Energy Finance found that Turkey could build a national clean energy market for roughly the same cost as its planned fleet of conventional coal plants, but with the added benefits of cleaner air, an improved balance of trade, more manufacturing jobs and lower carbon emissions. The same is true for so many countries around the world.

The recent climate agreement reached between the U.S. and China was an important step forward for global cooperation, because for the first time the world’s two largest energy users came together, formally recognized a shared interest in tackling the issue and made concrete climate-related commitments.

The conference in Lima offers a great opportunity for national leaders to build on that progress. Cities and businesses are natural partners for national governments. After all, most businesses are in cities and most cities are on coastal waters. Both have the incentives to mitigate the worst effects of climate change. And with the right tools, both can help lead the way toward the ultimate goal of a global climate agreement in Paris next year.

Agriculture, forestry and climate

After the energy sector, agriculture, forestry and other land use accounts for the largest amount of global greenhouse gas emissions – about 25%. The recent UN Climate Summit’s New York Declaration on Forests names soy, palm oil, beef and paper production as the cause of half of global deforestation – and calls for ending deforestation by 2030. If that goal is reached, it would be the equivalent to eliminating the GHG emissions of all the world’s cars or of the entire US economy.

Doing what works

A Rainforest Alliance delegation is presenting some of its work at COP 20 to reduce the impact of agriculture and forestry on the world’s climate, and increasing the sectors’ sustainability.

In Brazil, for example, the alliance has certified the first sustainable, deforestation-free cattle ranches and is promoting sustainable ranching. In the Andean Amazon it is demonstrating how different approaches can work together, from sustainable ranching in Colombia to commercial reforestation in Ecuador, to the sustainable harvest of timber and non-timber forest products, such as like palm fruit, in Peru.

These programs cut GHG emissions, protect Amazon forests and restore degraded land, and also improve agricultural productivity and the income and livelihood of rural producers that are feeling the impact of climate change directly.

Farmers at risk

People living on atolls and coastal flood zones aren’t the only ones displaced by climate change. Smallholder farmers, community foresters and others whose livelihoods depend on the land are also at risk. For example, climate change threatens coffee farmers’ way of life in Oaxaca, Mexico. Some farmers, such as Leandro Salinas, are retooling to grow climate-friendly coffee. In this video, Salinas says: “Even though we know we aren’t causing [climate change] – it’s others who are causing it – we, too, must do something.”

Farmers and foresters need finance, know-how and technology to cope with the impact of climate change. They also need incentives and viable alternatives to keep from clearing more forest for crops or timber. Without these things, deforestation is likely to increase, causing GHG emissions to rise.

The UN climate treaty process and the discussions under way in Lima recognizes this. The outcomes from COP 20 could include more support for regional and bilateral agreements, and for helping farmers and foresters work in sustainable, climate-smart ways. That could help lay the foundations for a global treaty in Paris at COP 21 to create a sustainable world economy.

Jeff Hayward is the director of Rainforest Alliance’s climate program. He’s currently leading a Rainforest Alliance delegation to the COP 20 meeting in Lima, Peru.

“If you don’t cut emissions, we’re just going to have to ask for more money because the damage is going to be worse,” Ronald Jumeau of the Seychelles said at U.N. climate talks.

The report was bound to sharpen disputes in Lima over who pays the bills for the impacts of global warming, whose primary cause is the burning of coal, oil and gas but which also includes deforestation. It has long been the thorniest issue at the U.N. negotiations, now in their 20th round.

Rich countries have pledged to help the developing world convert to clean energy and adapt to shifts in global weather that are already adversely affecting crops, human health and economies. But poor countries say they’re not seeing enough cash.

Projecting the annual costs that poor countries will face by 2050 just to adapt, the United Nations Environment Program report deemed the previous estimate of $70 billion to $100 billion “a significant underestimate.” It had been based on 2010 World Bank numbers.

The report says new studies indicate the costs will likely be “two to three times higher,” possibly even as high as $500 billion.

But that’s only if global warming stays below 2 degrees Celsius (3.2 degrees Fahrenheit) compared to pre-industrial times, the limit set in the U.N. talks. Scientists say that would require cuts in greenhouse gas emissions that the world is nowhere near on track to accomplish.

“The report provides a powerful reminder that the potential cost of inaction carries a real price tag,” UNEP director Achim Steiner said in a statement.

Climate change impacts, including rising sea levels, shifts in rainfall patterns and more intense heat waves, affect all countries but the latter aren’t well equipped to cope.

They need help to protect their shorelines, crops, and freshwater resources from rising seas, droughts and floods.

“We know what needs to be done. We just need the dollars or euros,” said Jumeau, who is also spokesman for small island states. The Seychelles is struggling to protect beaches from eroding, freshwater wells from drying up and coral reefs from being damaged, he said.

There is concern in Latin America that gains against poverty in the past two decades will be reversed due to climate change.

A World Bank study this year found two degrees of warming would cause crop yields in Brazil to drop by 30-70 percent for soy and 50 percent for wheat.

Rich countries have pledged to provide $100 billion by 2020 to help developing reduce their emissions and adapt to climate change. They are not on track to deliver. Their governments provided about $25 billion in adaptation money to developing countries in 2012-2013, the UNEP report said.

Jumeau noted that the U.S. Congress approved more than twice as much in a disaster aid package after Hurricane Sandy in 2012.

The talks’ host country, Peru, is one of the most vulnerable to climate change. Already, it faces diminished highland water supplies from melting glaciers and global warming has also hurt the fishing industry.

The U.N.’s World Food Program says 3 million Peruvians ? or one in 10 ? are highly vulnerable to food insecurity and natural disaster risks.

Yet, like most developing nations, what it spends on adapting to climate change, including highlands reservoirs and irrigation projects, will have to compete with other urgent needs, such as improving education, public health and public transport.

“There isn’t enough money and there aren’t resources specifically earmarked to finance adaptation in Peru,” said Lenkiza Angulo, who runs adaptation projects in the Andean nation funded by the Swiss government and valued at $11 million.

One vehicle for funding adaptation ? as well as mitigating damages from climate change ? is The Green Climate Fund, which nearly reached the $10 billion mark on Friday with a $258 million pledge from Norway.

New targets for fossil fuel use were announced ahead of the climate conference by the U.S., the European Union and China, the first Asian nation to make such a pledge. This has injected optimism into negotiations that are supposed to climax in Paris next year with the adoption of a long-awaited climate pact.

But India, Russia, Japan and Australia have yet to commit to new limits; and scientists say much sharper emissions cuts are needed in coming decades to keep global warming within 2 degrees C (3.6 F) of pre-industrial times, the overall goal of the U.N. talks. Global temperatures have already risen about 0.8 degrees C (1.3 F), and more heat-trapping gases are emitted every year.

Every degree of warming can cause long-lasting impacts, from melting ice caps and rising sea levels to the loss of species.

“Human influence on the climate system is clear,” Rajendra Pachauri, who leads the U.N.’s panel of climate-change experts, told delegates at the opening session in Lima on Monday.

To have a decent chance of reversing the warming trend before the planet hits the 2-degree mark, the world needs to slash emissions by 40 percent to 70 percent by 2050 and to near-zero by the end of the century, according to the panel’s assessments.

Scientists are practically united in warning that there’s no way to meet this goal by continuing business as usual.

It would require a sustained, permanent, worldwide shift from fossil fuels to renewable energy sources to power homes, cars and industries. And even then, the transition might not happen fast enough without a large-scale deployment of new technologies to remove greenhouse gases from the atmosphere.

“We call on the world to ensure the opportunity does not slip away,” said Nauru’s Marlene Moses, representing a group of Pacific island nations threatened by rising seas.

The biggest challenge for the U.N.-sponsored talks is dividing responsibilities between rich Western countries and emerging economies such as China and India. The poorest and most vulnerable nations also need help to develop their economies without aggravating global warming, and to adapt to climate changes that are already causing more violent weather, prolonged droughts and intense flooding.

Among them is host country Peru, whose glaciers are melting ever-faster, threatening water supplies on the coastal desert where 70 percent of its citizens live and threatening the nation’s hydropower and food security.

The negotiators in Lima are focusing on a draft agreement that can be refined before the Paris meeting a year from now.

A key issue is what data each government should provide so that formal emissions targets can be compared.

Developing countries also want rich nations to make good on promises of financing to reduce emissions and mitigate climate change impacts, which range from the spread of diseases to coastal flooding to major disruptions to agriculture.

There’s no common agreement on how that money should be used; for example, The Associated Press found that Japan has spent $1 billion of its climate financing on new power plants in Indonesia that burn coal — the top source of man-made emissions. Japan says it improves the environment because the new plans burn cleaner, but critics said coal has no place in climate financing.

The U.N.’s weather agency is expected to present temperature data showing 2014 could be the hottest year on record.

Peru is among the countries most affected. The Andean nation has 70 percent of the world’s tropical glaciers, which have lost more than a fifth of their mass in just three decades, putting 300,000 highlanders under severe stress as pastures and croplands dry up, the planting cycle becomes more erratic and cold snaps more severe. Lima is the world’s second-largest desert capital after Cairo, Egypt, and its 10 million inhabitants depend on glacial runoff for hydropower and to irrigate crops.

Latin America and the Caribbean cause less than 10 percent of global emissions, and yet its people are already shouldering and oversized burden. Climate change is blamed for the extinction of plants and animals in Andean cloud forests and for damaging offshore fisheries. Even if warmer weather benefits industrial agriculture in some places, more people are expected to go hungry as subsistence farming suffers.

The regional economic damage from all this will reach $100 billion a year by mid-century, according to research done for the Inter-American Development bank.

“The people with the least intensive climate lifestyles are suffering the most,” said geographer Jeffrey Bury of The University of California at Santa Cruz, who studies the social and economic impacts of glacier loss.

“I think we can use the Andes high mountain environment,” he said, “to understand what the future holds for the rest of us.”

The numbers are stark. Carbon dioxide emissions: up 60 percent. Global temperature: up six-tenths of a degree. Population: up 1.7 billion people. Sea level: up 3 inches. U.S. extreme weather: up 30 percent. Ice sheets in Greenland and Antarctica: down 4.9 trillion tons of ice.

“Simply put, we are rapidly remaking the planet and beginning to suffer the consequences,” says Michael Oppenheimer, professor of geosciences and international affairs at Princeton University.

Diplomats from more than 190 nations opened talks Monday at a United Nations global warming conference in Lima, Peru, to pave the way for an international treaty they hope to forge next year.

To see how much the globe has changed since the first such international conference – the Earth Summit in Rio de Janeiro in 1992 – The Associated Press scoured databases from around the world. The analysis, which looked at data since 1983, concentrated on 10-year intervals ending in 1992 and 2013. This is because scientists say single years can be misleading and longer trends are more telling.

Our changing world by the numbers:

WILD WEATHER

Since 1992, there have been more than 6,600 major climate, weather and water disasters worldwide, causing more than $1.6 trillion in damage and killing more than 600,000 people, according to the Centre for Research on the Epidemiology of Disasters in Belgium, which tracks the world’s catastrophes.

While climate-related, not all can be blamed on man-made warming or climate change. Still, extreme weather has noticeably increased over the years, says Debby Sapir, who runs the center and its database. From 1983 to 1992 the world averaged 147 climate, water and weather disasters each year. Over the past 10 years, that number has jumped to an average 306 a year.

In the United States, an index of climate extremes – hot and cold, wet and dry – kept by the National Oceanic and Atmospheric Administration has jumped 30 percent from 1992 to 2013, not counting hurricanes, based on 10-year averages.

NOAA also keeps track of U.S. weather disasters that cost more than $1 billion, when adjusted for inflation. Since 1992, there have been 136 such billion-dollar events.

Worldwide, the 10-year average for weather-related losses adjusted for inflation was $30 billion a year from 1983-92, according to insurance giant Swiss Re. From 2004 to 2013, the cost was more than three times that on average, or $131 billion a year.

Sapir and others say it would be wrong to pin all, or even most, of these increases on climate change alone. Population and poverty are major factors, too. But they note a trend of growing extremes and more disasters, and that fits with what scientists have long said about global warming.

It’s this increase that’s “far scarier” than the simple rise in temperatures, University of Illinois climate scientist Donald Wuebbles says.

TEMPERATURE

It’s almost a sure thing that 2014 will go down as the hottest year in 135 years of record keeping, meteorologists at NOAA’s National Climatic Data Center say. If so, this will be the sixth time since 1992 that the world set or tied a new annual record for the warmest year.

The globe has broken six monthly heat records in 2014 and 47 since 1992. The last monthly cold record set was in 1916.

So the average annual temperature for 2014 is on track to be about 58.2 degrees (14.6 degrees Celsius), compared with 57.4 degrees (14.1 degrees Celsius) in 1992. The past 10 years have averaged a shade below 58.1 degrees (nearly 14.5 degrees Celsius) – six-tenths of a degree warmer than the average between 1983 and 1992.

THE OCEANS

The world’s oceans have risen by about 3 inches since 1992 and gotten a tad more acidic – by about half a percent – thanks to chemical reactions caused by the absorption of carbon dioxide, scientists at NOAA and the University of Colorado say.

Every year sea ice cover shrinks to a yearly minimum size in the Arctic in September – a measurement that is considered a key climate change indicator. From 1983 to 1992, the lowest it got on average was 2.62 million square miles. Now the 10-year average is down to 1.83 million square miles, according to the National Snow and Ice Data Center.

That loss – an average 790,000 square miles since 1992 – overshadows the slight gain in sea ice in Antarctica, which has seen an average gain of 110,000 square miles of sea ice over the past 22 years.

ON LAND

The world’s population in 1992 was 5.46 billion. Today, it’s nearly a third higher, at 7.18 billion. That means more carbon pollution and more people who could be vulnerable to global warming.

The effects of climate change can be seen in harsher fire seasons. Wildfires in the western United States burned an average of 2.7 million acres each year between 1983 and 1992; now that’s up to 7.3 million acres from 1994 to 2013, according to the National Interagency Fire Center.

And some of the biggest climate change effects on land are near the poles, where people don’t often see them. From 1992 to 2011, Greenland’s ice sheet lost 3.35 trillion tons of ice, according to calculations made by scientists using measurements from NASA’s GRACE satellite. Antarctica lost 1.56 trillion tons of ice over the same period.

THE AIR

Scientists simply point to greenhouse gas emissions, mostly carbon dioxide, that form a heat-trapping blanket in our air.

There’s no need to average the yearly amount of carbon dioxide pollution: It has increased steadily, by 60 percent, from 1992 to 2013. In 1992, the world spewed 24.9 billion tons of carbon dioxide; now it is 39.8 billion, according to the Global Carbon Project, an international consortium.

China has tripled its emissions from 3 billion tons to 11 billion tons a year. The emissions from the U.S. have gone up more slowly, about 6 percent, from 5.4 billion tons to 5.8 billion tons. India also has tripled its emissions, from 860 million tons to 2.6 billion tons. Only European countries have seen their emissions go down, from 4.5 billion tons to 3.8 billion tons.

WHAT SCIENTISTS SAY

“Overall, what really strikes me is the missed opportunity,” Andrew Dessler, a climate scientist at Texas A&M University, said in an email.

“We knew by the early 1990s that global warming was coming, yet we have done essentially nothing to head off the risk. I think that future generations may be justifiably angry about this.”

“The numbers don’t lie,” said Michael Mann, a climate scientist at Penn State. “Greenhouse gases are rising steadily and the cause is fossil fuel burning and other human activities. The globe is warming, ice is melting and our climate is changing as a result.”