How quickly humanity draws down the greenhouse gases driving global warming will determine whether sea levels rise half-a-metre or six times that, even if Paris climate pact goals are fully met, researchers reported Tuesday in a study.
“The trajectory of emissions in the next few decades will shape our coastlines in the centuries to come,” lead author Matthias Mengel, a scientist at the Potsdam Institute for Climate Impact Research in Germany, told AFP.
Every five years that elapse before carbon pollution peaks will add 20 centimetres to sea level rise in 2300, the study found.
“This is the same amount we have experienced so far since the beginning of the fossil fuel economy,” Mengel said by email.
The world collectively spews about 40 billion tonnes of CO2 into the atmosphere every year. After stalling for three years, emissions rose by two percent in 2017, dashing hopes they had peaked.
On current trends, emissions could increase for at least another decade.
The 197-nation Paris Agreement calls for capping global warming at “well below” two degrees Celsius (3.6 degrees Fahrenheit), and pursuing efforts to hold the line at 1.5 C.
Average global temperatures have already gone up by 1 C since the industrial revolution began.
The treaty also sets a less talked about but equally crucial goal: ensuring that, by the end of this century, our species stops adding CO2 to the atmosphere, a threshold known as “net zero emissions”.
Mengel and colleagues asked a deceptively simple question: by how much will the world’s oceans rise over the next two centuries if both these targets are achieved?
The most likely outcome, they found, was an increase of 70 to 120 centimetres (27.5 to 47 inches) by 2300, depending on when CO2 pollution peaks, how quickly it drops, and the date net zero emissions is achieved.
That’s probably enough to doom some low-lying island states and wreak havoc in the populated mega-deltas of Bangladesh, Vietnam, India and Egypt, but would at least leave more time to adapt.