A REVIEW OF THE SCIENCE

How much will the average temperature of the planet increase? That depends on us. First, remember that making projections about the future, especially for something as complex as the entire Earth’s ecosystem, is challenging. As scientists measure more and more data points, they become more confident about the accuracy or likelihood of their predictions. Most projections of future temperatures present several scenarios, the course we are currently on (also known as the “business as usual” scenario), then projections of temperature increases based on collective action humanity may take to reduce greenhouse gas (GHG) emission that cause climate change. Below is an example of this from Climate Action Tracker.

The solid black line represents the actual Gigatons of CO2 equivalent emissions emitted globally. The gray band then represents the “business as usual” trajectory (with more error or uncertainty as the projections get further into the future). This would lead to 4.1-48° C warming by 2100. The darker blue band represents emissions reductions and subsequent temperature estimates if current policies are implemented and effective. This would lead to a 2.8-3.2° C rise. The light blue band is based on commitments nations have made under the Paris Accord. The yellow and light green bands show how dramatically we would need to reduce emission to limit the increase in temperature to 1.5 and 2.0 degrees respectively.

If current policies are fully implemented and work as hoped, the planet is projected to still warm between 2.8 – 3.2° C above pre-industrial levels by 2100. That is still dangerously warmer than in any conditions humans have ever lived.

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