were releasing ever-increasing amounts of CO2 and other heat-trapping gases into the atmosphere.
The graph they created, which was used in the IPCC’s Third Assessment Report, in 2001, looked like a hockey stick, with a long, steady line that took a sudden jump upward at the end. Although many other scientists confirmed the results, Mann’s work became a target for those opposed to prevailing theories of anthropogenic climate change. Attackers included politicians, pundits, a few scientists, and two Canadians: former mining company executive and consultant Steve McIntyre and economist Ross McKitrick. Although subsequent research found that the Canadians were correct in pointing out some statistical errors, the failings were minor and did not significantly affect the overall results. Several studies found more serious errors in McKitrick and McIntyre’s methodology, and dozens of subsequent studies using various methods and records have since confirmed Mann’s original analysis, with only slight variations.
Another report by aerospace engineer Willie Soon and astronomer Sallie Baliunas, published in the journal Climate Research, claimed that the Northern Hemisphere was warmer during the medieval period than Mann estimated, but their methodology and data, and the publication’s peer-review process, were found to be lacking, leading to the resignation of several of the journal’s editors and an admission by the publisher that the article should not have been accepted as is. Soon has received much of his funding from fossil fuel companies, and Baliunas has been affiliated with a number of fossil fuel–funded organizations.
As Mann told Scientific American in 2005, “From an intellectual point of view, these contrarians are pathetic, because there’s no scientific validity to their arguments whatsoever. But they’re very skilled at deducing what sorts of disingenuous arguments and untruths are likely to be believable to the public that doesn’t know better.”4
The IPCC and Global Efforts
IN RESPONSE TO the increasing knowledge—and alarm—about global warming, the World Meteorological Organization and UN Environment Programme set up the Intergovernmental Panel on Climate Change in 1988 at the request of member governments. According to the IPCC website, its goal was “to prepare a comprehensive review and recommendations with respect to the state of knowledge of the science of climate change; the social and economic impact of climate change, and possible response strategies and elements for inclusion in a possible future international convention on climate.” Under its governing principles, its assessments were to be “comprehensive, objective, open and transparent”; based on scientific evidence; and “neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.”
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
