The climate science you missed
THE UN Intergovernmental Panel on Climate Change (IPCC) report published in August ran to almost 4,000 pages, and it alone contains enough material to fill five years of science-you-missed columns. Don’t be fooled by its size, though. Climate change is still a simple problem with a conceptually simple solution.
This message is spelled out in a single sentence in an IPCC summary report, all 41 pages of which required unanimous, word-by-word agreement among 195 nations: “[T] here is a near-linear relationship between cumulative anthropogenic CO2 emissions and the global warming they cause.”
What that means is every metric ton of a greenhouse gas emitted heats up the atmosphere a little bit-and every ton avoided prevents it. The updated models confirming this work are descendants of the half-centuryold breakthroughs that finally won the Nobel Prize in Physics in 2021.
Knowing that CO2 and temperature travel almost in lockstep is what allowed IPCC scientists for the first time in 2013 to introduce their “carbon budget,” a conceptual tool that helps the rest of us keep track of how close we are to blowing past the global safety goals set in 2015 in Paris.
CO2 emissions from 1850 to 2019 totalled 2,390 billion tons. To have a 50 per cent chance of limiting the temperature rise to 1.5 C, emissions from 2020 and onward must stay below 500 billion tons. That’s a margin of about 13 years at the current emissions rate. Despite an historic pandemic-related drop, CO2 emissions from fossil fuels and land use last year totalled 39 billion tons, with a strong rebound expected this year.
Global emissions have yet to peak, let alone fall at the necessary estimated rate, which was calculated in 2019 to be 7.6 per cent a year. (It’s even higher now.) Oil and gas production must fall 3 per cent a year globally through 2050 to meet the 1.5 C goal.
Perhaps the torpid pace of humanity’s response pushed the IPCC authors (hundreds of them, unpaid) to emphasize emissions-cutting strategies, which are the focus of a subsequent report. The scientists speak about carbon dioxide removal without favouring any singular approach to reducing its atmospheric concentrations. Approaches include catching and storing CO2 from smokestacks and open air, tree planting, and mineral absorption. Quickly cutting methane emissions, which make up more than a quarter of greenhouse gas emissions, would both slow down global heating and improve air quality. Satellites are increasingly able to spot areas of high methane emissions, such as US and Russian oil and gas production.
Everywhere, people are experiencing new weather extremes. Since the last IPCC science report in 2013, researchers have honed the ability to estimate how much climate change has influenced individual events (page 58).
Just this past summer, a leading scientific group found the deadly North American Pacific heat wave in June would have been “virtually impossible” without greenhouse gas pollution. It was a real-life example of research published weeks later projecting that heat records will continue to be set by higher margins as the years go by.
Many of the scientific observations about global change can be thought of as symptoms. Researchers at United Nations University (UNU), an international think tank with centres in 12 countries, want to elevate awareness of the systemic root causes of meteorological and other types of tragedies. These causes include greenhouse gas pollution, poor disaster risk management, and economic analysis that ignores environmental costs and benefits. Their inaugural annual report in September, Interconnected Disaster Risks, compared how 10 disasters in 2020 share several causes. The events include flooding in Vietnam, freshwater fish extinction in China, the February 2020 cold-weather disaster in Texas, and the August 2020 Beirut explosion. The subjects of the UNU study go beyond those the IPCC addressed, but the lesson is the same. “It conveys the message that we messed up. There’s still a last window of opportunity we can take, but we need to take it now,” says Zita Sebesvari, an environmental scientist and a lead author.
The interlocking crises of global warming and biodiversity loss motivated more than 200 medical journals around the world to publish a commentary arguing that “the greatest threat to global public health is the continued failure of world leaders to keep the global temperature rise below 1.5 C and to restore nature.”
Should nations’ failure to constrain emissions continue, and the heating consequently worsen, the safest people may be those living in rich areas or in “collapse lifeboats,” places such as New Zealand or Iceland, remote and not overpopulated temperate islands with their own agriculture and industry. Climate science is so mature, and government inaction has made risks so pronounced, that the useful scientific questions now concern how to adapt.