Summary of October 2018 IPCC report, Global Warming of 1.5 Degrees
If the Earth warms by just 1.5°C over preindustrial times by 2100, rather than 2°C, we would see fewer extremes of life-threatening heat, drought and precipitation, less se level rise, and fewer species lost. These findings are detailed in the report of the Intergovernmental Panel on Climate Change, released October 8, 2018.
The paper is the result of scientists calling for more careful study of the Paris Agreement (2015) to curb greenhouse gas emissions sufficiently to limit global warming to "well below" 2°C by 2100. During the talks many nations called for a lower target of 1.5°C and many scientists have since warned that 2°C isn't low enough to prevent major environmental changes.
91 scientists from 40 countries reviewed more than 6000 papers probing the impact of a global temperature hike of 1.5°C. They found that the difference between 1.5 and 2°C is stark. Half a degree less warming means about 0.1 meters less sea level rise on average by 2100, resulting in 10 million fewer people exposes to risks of flooding, infrastructure damage, and saltwater intrusion into freshwater resources.
As temperatures approach 2°C, ice sheets become increasingly unstable, further increasing the potential for sea level rise and other harmful effects. With 1.5°C warming the Arctic Ocean is projected to be ice-free in the summer once a century. At 2°C , it would be ice free once a decade.
For many plant and animal species, 1.5°C would mean less risk of habitat loss. Risks of forest fires, spread of invasive species, extreme weather events, droughts, and floods would also be less.
To keep warming to 1.5°C requires reducing emissions by about 45% relative to 2010 levels by 2030 and reaching net zero (the point at which the amount of carbon released to the atmosphere is balanced by the amount removed) by about 2050. To hold warming to below 2°C, emissions must decline by about 20 percent by 2030 and reach net zero by about 2075.
If we do not make these early, deep cuts in emissions, it will take "negative emissions" to bring the temperature back down after overshooting the mark. Negative emissions depend on future technologies (that are not yet proven or commercially viable) that can remove carbon dioxide from the atmosphere.
The report emphasizes that holding warming to 1.5°C is not impossible, but does require emissions cuts to start now and requires behavioral changes from diet to energy conservation.
This video is useful as well.
Diane Shisk