Even if humans could instantly turn off all听emissions of greenhouse gases,听Earth would continue to heat up about two more degrees Fahrenheit by the turn of the century, according to a sophisticated new analysis听听in the journal听Nature Climate Change.
If current emission rates continue for 15 years, the research shows, odds are good that the planet will see nearly three degrees Fahrenheit (1.5 Celsius) of warming by then.
鈥淭his 鈥榗ommitted warming鈥� is critical to understand because it can tell us and policymakers how long we have, at current emission rates, before the planet will warm to certain thresholds,鈥� said Robert Pincus, a scientist with the听, a partnership of听the 麻豆视频 and NOAA. 鈥淭he window of opportunity on a 1.5-degree [C] target is closing.鈥�
During United Nations meetings in Paris last year, 195 countries including the United States signed an agreement to keep global temperature rise less than 3.5 degrees F (2 C)听above pre-industrial levels, and pursue efforts that would limit it further, to less than 3 degrees Fahrenheit (1.5 C) by 2100.
The new assessment, co-authored听by Pincus and Thorsten Mauritsen of the Max Planck Institute for Meteorology, is unique in that it does not rely on computer model simulations, but rather on observations of the climate system to calculate Earth鈥檚 climate commitment. Their work accounts for the capacity of oceans to absorb carbon, detailed data on the planet鈥檚 energy imbalance, the climate-relevant behavior of fine particles in the atmosphere听and other factors.
Among Pincus and Mauritsen鈥檚 findings:
- Even if all fossil fuel emissions stopped in 2017, warming by 2100 is very likely to reach about 2.3 F (range: 1.6-4.1) or 1.3 degrees C (range: 0.9-2.3).
- Oceans could reduce that figure a bit. Carbon naturally captured and stored in the deep ocean could cut committed warming by 0.4 degrees F (0.2 C).
- There is some risk that warming this century cannot be kept to 1.5 degrees C beyond pre-industrial temperatures. In fact, there is a 13 percent chance we are already committed to 1.5-C warming by 2100.
鈥淥ur estimates are based on things that have already happened, things we can observe, and they point to the part of future warming that is already committed to by past emissions,鈥� said Mauritsen. "Future carbon dioxide emissions will then add extra warming on top of that commitment.鈥�
The research was funded by the Max-Planck-Gesellschaft, the U.S. Department of Energy and the National Science Foundation.听
