World may warm by 25 per cent more than current projections suggest
'Official' projections for how much the world will warm are already catastrophic, and now it appears they significantly underestimate future warming
Recent climate models have been questioned as potentially inaccurate, but a novel method of evaluating these models indicates they may have overestimated temperature increases. According to Gergana Gyuleva of ETH Zurich in Switzerland, for a specific carbon dioxide emission rate, global warming could be 25% greater than initially anticipated.
This revelation carries significant consequences. The Climate Action Tracker, for example, now anticipates a 3.25°C rise in average global surface temperatures by 2100, instead of the previously projected 2.6°C. The extent of global warming hinges on the additional CO2 released into the atmosphere and the planet's response to that CO2.
Different climate models yield varying estimates for temperature increases when CO2 levels double. Some models predict a 1.6°C temperature rise, while others suggest a potential increase of up to 3°C. Determining which models are accurate is crucial, as the range can have substantial implications. Traditionally, this task involved comparing climate models' projections of recent climate responses to actual historical data.
Models that projected more warming than occurred were discarded. The Intergovernmental Panel on Climate Change's last report, based on these assessments, concluded that a doubling of CO2 would result in a 1.2°C to 2.4°C temperature increase, with a best estimate of 1.8°C. However, Earth's climate exhibits considerable variability.
For instance, during La Niña, cooler deep ocean water rises to the surface, leading to reduced global surface temperatures. To address this, Gyuleva and her colleagues filtered the historical climate record to eliminate the impact of such natural variability. This adjustment, which focused on the period 1981 to 2014 (a time when a noticeable slowdown in global warming was observed), resulted in higher estimates of temperature increases from a CO2 doubling.
Additionally, Gyuleva's team assessed models using emerging satellite data that measures incoming solar radiation and outgoing long-wave radiation. The disparity between these measurements serves as a fundamental gauge of global warming. By evaluating models based on their accuracy in projecting these radiation trends, the team found that those best matching observed trends projected considerably higher temperature increases.
Based on this refined analysis, Gyuleva's team concludes that a doubling of CO2 could lead to a 1.9°C to 2.6°C temperature rise, with a best estimate of 2.25°C. While further confirmation from additional sources is necessary, this approach appears promising. Steven Sherwood at the University of New South Wales in Sydney acknowledges the value of removing natural variability from the analysis but questions the effectiveness of using short-wave and long-wave radiation trends to assess models.
Nonetheless, the recent surge in temperature trends may lead to higher estimated ranges, regardless of the assessment method. In climate terminology, this refined estimate is termed the transient climate response, representing one of three types of climate sensitivity, each varying in timescale.
Written by urgent.news from New Scientist's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
