Climate Change Tracker: How much will the earth heat up with rising CO2 levels?
A landmark new study says that if carbon dioxide levels in the atmosphere double from pre-industrial times, then the earth will heat up by a catastrophic 2.6 to 4.1 degrees Celsius
All work on combating the climate crisis, be it the research done by climate scientists, or the global attempts at mitigation spearheaded by the United Nations, is based on one key formulation. When carbon dioxide levels in the atmosphere are double that of pre-industrial times, about 200 years ago, how will the earth’s climate change? More specifically, by how much will the global average temperature rise from pre-industrial times? This is called climate sensitivity, and this range of possible temperature rise is what our understanding of global heating is based on.
This range, of 1.5-4.5 degrees Celsius, was established in a landmark study from 1979 titled Carbon Dioxide And Climate: A Scientific Assessment. All subsequent advances in climate science have been informed by the range established by this report. For the last four decades, however, scientists have been trying to narrow down this wide range of temperatures. This finally happened, when, last week, a multidisciplinary study by scientists from 20 climate institutions from around the world, was published. According to An Assessment Of Earth’s Climate Sensitivity Using Multiple Lines Of Evidence, a doubling of CO2 levels will lead to a temperature rise of 2.6-4.1 degrees Celsius.
Click here to listen to the latest episode of the Mint Climate Change Tracker podcast, hosted by Bibek Bhattacharya.
The scientists combined recorded temperature from the time of the industrial revolution, prehistoric temperature records from tree rings and soil sediments and modern climate models and satellite data to arrive at the range. This finding, of a 66% chance of a 2.6-3.9 degree rise, shows us that the crisis is much graver than we think. While the chances of an upper limit of heating of 5 degrees or more is low, this range is bad enough.
The Intergovernmental Panel on Climate Change (IPCC) and the UN Framework Convention on Climate Change (UNFCCC) are guided by the optimistic hope of limiting warming to a 1.5-2 degree rise by 2100. This now seems like an incredibly hard goal to reach in light of this study’s findings. The need to drastically cut carbon emissions just became more urgent.
The point to remember is that just a 2 degree Celsius rise in the planet's temperature is bad enough. The UK-based climate website Carbon Brief distilled the findings of over 70 studies into an in-depth infographic to show what a 2 degree rise would mean. On average, this would mean a 56cm rise in global sea levels, with marine heatwaves increasing 23 times in frequency, killing all coral reefs. Eighty per cent of Arctic summer ice would be gone, with the number of hot days increasing by 25%. Over a quarter of humanity would face intense heatwaves every five years; 388 million people would suffer from water scarcity, and over 194 million people from severe drought.
And that’s just the tip of the iceberg. The planet is already 1.2 degrees Celsius hotter than pre-industrial times. The atmospheric CO2 level, according to the US National Oceanic and Atmospheric Administration (NOAA) is currently 417 ppm (parts per million), up from 280 ppm in pre-industrial times. And it’s rising by 2.5 ppm per year. The dreaded figure of 560ppm, i.e. double the atmospheric carbon from pre-industrial times, doesn't seem so far away. An immediate move away from fossil fuel energy is more urgent than ever.
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FIRST PUBLISHED30.07.2020 | 10:00 AM IST