Its First Assessment Report, in 1990, provided much of the impetus for the formation of the United Nations Framework Convention on Climate Change (UNFCCC), “the key international treaty to reduce global warming and cope with the consequences of climate change.” It has since produced many comprehensive assessment reports, including the 1995 Second Assessment that provided materials used by negotiators for preparation and adoption of the Kyoto Protocol in 1997. The Third Assessment was released in 2001 and the Fourth in 2007. The IPCC was awarded the Nobel Peace Prize in 2007.
With each assessment, the science has become more robust, and the number of scientists, writers, and contributors has grown to include experts from around the world, with topics covered becoming increasingly broad.
The Fifth Assessment Report was released from September 2013 to November 2014 in four chapters (1. current science, 2. impacts, 3. strategies to deal with the problem, and 4. a final report synthesizing the three chapters). It showed more scientific certainty than in 2007, when the Fourth Assessment was released, that humans are largely responsible for global warming—mainly by burning fossil fuels and cutting down forests—and that it’s getting worse and poses a serious threat to humanity. It contained hints of optimism, though, and showed that addressing the problem creates opportunities.
Scientists are cautious. That’s the nature of science; information changes, and it’s difficult to account for all interrelated factors in any phenomenon, especially one as complicated as global climate. When they say something is “extremely likely” or 95 percent certain—as the Fifth Assessment Report did regarding human contributions to climate change—that’s as close to certainty as science usually gets. Evidence for climate change itself is “unequivocal.”
The first chapter alone cited 9,200 scientific reports in 2,200 pages, stating, “It is extremely likely that human activities caused more than half of the observed increase in global average surface temperature from 1951 to 2010.” It also concluded that oceans have warmed, snow and ice have diminished, sea levels have risen, and extreme weather events have become more common.
The report also dismissed the notion, spread by climate change deniers, that global warming has stopped. It was thought to have been slowing slightly because of natural weather variations and other possible factors, including increases in volcanic ash, changes in solar cycles, and oceans absorbing more heat. But improvements in methods to measure sea surface temperatures led the U.S. National Oceanic and Atmospheric Administration (NOAA) to conclude in 2015 that oceans were warmer from 1998 to 2014 than previously thought and that a much-touted slowing or hiatus in warming didn’t occur.5 That study itself was challenged by a February 2016 study published in Nature Climate Change, which did find evidence of a slowdown in the rate of warming, though not a halt.6 It also found the slowdown has probably ended. One thing the scientists and their studies confirm is that none of it means climate change is any less of a worry. In fact, the warmest ten years have all been since 1998 (itself an unusually warm year, and one that deniers have desperately cherry-picked as a starting point to claim that warming stalled), and in 2013, carbon dioxide levels rose by the highest amount in thirty years.
According to the IPCC Fifth Assessment Report, an increase in global average temperatures greater than 2 degrees Celsius above preindustrial levels would be catastrophic, resulting in further melting of glaciers and Arctic ice, continued rising sea levels, more frequent and extreme weather events, difficulties for global agriculture, and changes in plant and animal life, including extinctions. The report concluded we’ll likely exceed that threshold this century, unless we choose to act. Subsequent research has shown that 2 degrees is too conservative and that warming over 1.5 degrees will probably lead to disaster. We’re almost at 1 degree already!
The reasons to act go beyond averting the worst impacts of climate change. Fossil fuels are an incredibly valuable resource that can be used for making everything from medical supplies to computer keyboards. Wastefully burning them to propel solo drivers in cars and SUVs, and other inefficient energy uses, will ensure we run out sooner rather than later.
Nations working together to meet science-based targets to cut global warming pollution and create clean, renewable energy solutions would allow us to use our remaining fossil fuel reserves more wisely and create lasting jobs and economic opportunities. Energy conservation and clean fuels offer the greatest opportunities. Conserving energy makes precious nonrenewable resources last longer, reduces pollution and greenhouse gas emissions, saves consumers money, and offers many economic benefits.
Shifting to cleaner energy sources would also reduce pollution and the environmental damage that comes with extracting coal, oil, and gas. That would improve the health of people, communities, and ecosystems, and reduce both health care costs and dollars spent replacing services nature already provides with expensive infrastructure. Reducing meat consumption, which contributes to global warming, is also beneficial to human health.
The fast-growing clean energy and clean technology sectors offer many benefits. Improved performance and cost reductions make large-scale deployment for many clean energy technologies increasingly feasible. Worldwide spending on clean energy in 2013 was $207 billion.
By 2014, Germany, the world’s fourth-largest economy, was getting a third of its energy from renewable sources and had reduced carbon emissions 23 percent from 1990 levels, creating 370,000 jobs.
The 2015 Paris Agreement
FROM THE END of November to December 12, 2015, government ministers, negotiators, climate experts, and world leaders convened in Paris, France, to consider the implications of the IPCC’s Fifth Assessment Report and to agree on how to deal with its findings. It may well have been the world’s last chance for a meaningful agreement to shift from fossil fuels to renewable energy before ongoing damage to the world’s climate becomes irreversible and devastating.
The nations that met in Paris are responsible for more than 95 percent of global emissions. Although it’s far from perfect, the agreement they came up with marks a significant achievement. When nations last attempted a global climate pact—in 2009, at COP15 in Copenhagen, Denmark—negotiations broke down and the resulting declaration was considered a failure. The Paris Agreement, in process and outcome, was a dramatic improvement—a product of the growing urgency to act on the defining issue of our time. It’s the first universal accord to spell out ways to confront climate change, requiring industrialized nations to transition from fossil fuels to 100 percent renewable energy by 2050 and developing nations by about 2080.
Before meeting in Paris, governments drafted plans to reduce national carbon emissions beginning in 2020. One goal of the negotiations was to develop a review mechanism to encourage countries to improve targets over time. That was achieved, giving hope that reductions will keep global temperatures from rising more than 2 degrees Celsius above preindustrial levels. In fact, the newly revised limit of 1.5 degrees is acknowledged as a target for future goal setting. Although the commitments aren’t enough to achieve either goal, improving targets every five years—as is called for in the pact—will get us closer. Past experience shows that once a commitment is made to address a crisis, many unexpected opportunities and solutions arise.
Still, getting the world back on track will not be an easy task, especially as it requires action on commitments from nations that haven’t always lived up to their word. The world’s largest greenhouse gas emitter, China, was criticized throughout the conference for trying to water down requirements for a common emissions-and-targets reporting system and opposing the requirement for countries to update emissions-reduction goals every five years, advocating instead for