Established in 1988 by the UN and the World Meteorological Organization, the Intergovernmental Panel on Climate Change (IPCC) is a scientific body that periodically summarizes the scholarly understanding of the world’s climate. In 2007, the panel’s fourth assessment report outlined in stark terms the likelihood of anthropogenic global warming. Since then, severe storms and drought have ravaged North America, Australia and Africa, yet unusually wet, cold conditions have accompanied some European winters. Through it all carbon emissions have continued to rise, now driven largely by developing nations. Today, the IPCC’s highly anticipated summary for policymakers was finally released, in lieu of its fifth assessment report that will be published later this year. In this article, I explore this landmark report and the responses it has inspired from the perspective of a climate historian.
Initially, the most striking aspect of the IPCC’s new summary for policymakers was not its content but the media reaction. The banner at CNN is currently: “A town that’s melting.” Its subheading: “climate change already happening in Alaska town.” Additional titles announce: “climate change: it’s us,” and “Miama’s rising water,”while an opinion calls for “common sense.” Not surprisingly, among major news networks the BBC has provided the most informative analysis of the IPCC’s report, and its banner, while not as large as CNN’s, nevertheless reads: “UN ‘95% sure’ humans cause warming.” Of course, the Fox News headline is in substantially smaller font, and its conclusion is characteristically fair and balanced: “Hockey Schtick: UN report ignores global warming pause.” Worse still is coverage given by the Times of India, which features only a link in diminutive font buried at the bottom of its website. Meanwhile the homepage for CCTV, a major Chinese broadcaster, contains no reference at all to the report. Taken together, headlines at the big media outlets confirm the enduring importance of partisan divisions in the global warming discussion. They also suggest that scholars, journalists, the IPCC, and indeed the UN must do more to raise awareness of global warming in countries that will be most affected by its consequences. Still, the banner headlines on many centrist news outlets in the West are encouraging.
For those who have paid heed to the relentless debate about global warming, much of the action in the IPCC's fifth summary for policymakers happens in the first few pages. In previous days and weeks, so-called climate “skeptics” flooded the airwaves, encouraging rampant speculation about whether the alleged “pause” in global warming would feature prominently in the IPCC's new report. In fact, in its second page the IPCC's summary actually confirms that:
Not surprisingly, skeptics eager to discredit the scientific consensus around global warming have ignored these questions. Instead, they have arbitrarily started their climatic reconstructions at 1998, a year of extreme warmth, in order to highlight supposed cooling since then. Unfortunately for them, the scholars of the IPCC have included this paragraph:
The IPCC's summary for policymakers also addresses climates in the more distant past. Another argument frequently advanced by skeptics holds that the Medieval Climate Anomaly - previously known as the Medieval Warm Period - was actually accompanied by hotter temperatures than we face today. Their conclusion is that modern warming isn't a big deal, and falls within natural variability. Of course, the cause of current warming is more important to climate scientists than the scale of warming to date, because it is precisely that cause which will trigger future warming far beyond anything humanity has encountered. Nevertheless, the IPCC's report also discredits the idea that medieval warmth exceeded or matched modern temperatures:
The IPCC's fifth summary concludes that warming in the coming century will likely fall between 1.5-4 degrees Celsius. Moreover, it is more likely that warming will exceed a catastrophic 6 degrees Celsius than fall beneath 1 degrees Celsius. The lower range of this estimate is 0.5 degrees Celsius lower than it was in the IPCC's fourth assessment in 2007, owing in part to the slight divergence between model projections and climatic trends in the past decade. It is possible that the range will be adjusted upward in the IPCC's next report, as model simulations and average global warming converge again. Either way, our best guess for the future hasn't changed much: we probably face warming of approximately 3 degrees Celsius worldwide by the end of the century.
Climate scientist Michael Mann, author of The Hockey Stick and the Climate Wars, measures claims by climate skeptics in light of the IPCC's fifth summary for policymakers.
On September 28th, the scientists of the International Geosphere-Biosphere Programme respond to the IPCC's fifth summary.