Under the Paris Climate Agreement of 2015, more than 190 countries pledged to keep the global temperature less than 1.5 degrees Celsius above the average during the preindustrial period of 1850 to 1900. This period was before humans altered the atmosphere and the climate by emitting billions of tons of fossil fuel emissions and other pollutants. The level was chosen because climate models indicated that warming further would greatly intensify extreme weather events, ecosystem losses, and even potential submersion of small island countries.
Current projections are that global temperatures will exceed the 1.5 degree increase on an ongoing basis within a few years. Of even greater concern is that once the global temperature is more than about 1.7 or 1.8 degrees higher, it may be nearly impossible to return below the 1.5-degree threshold level. This overshoot zone entails new dangers. Such high temperatures could push melting ice sheets and key heat-carrying ocean currents past tipping points that would be difficult or even impossible to reverse on any human timescale.
The original Paris agreement sought to begin to cut greenhouse gas emissions immediately, halve them by 2035, and also find ways to remove billions of tons of carbon dioxide from the atmosphere.
In order to avoid catastrophic climate effects, scientists warn that any overshoot in global temperature should be as small and short-lived as possible. It is essential to limit how high temperatures rise and how long they remain above 1.5 degrees Celsius.
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References:
Climate ‘Overshoot’ Is Coming—Are We Ready?
