Emissions slashed today won’t slow warming until mid-century - The Economist

MUCH OF the international effort thus far to combat climate change has focused on cutting emissions of greenhouse gases, chief among them carbon dioxide.

But greenhouse-gas emissions do not cause an instantaneous rise in global temperatures, and neither does cutting them result in instantaneous cooling.

Using climate models, Bjorn Samset and his colleagues at Norway’s Centre for International Climate Research probed hypothetical futures in which emissions of nine different industrial pollutants, including carbon dioxide and methane, were either eliminated instantly or phased out at a rate of 5% each year, starting in 2020.

Running these simulations over and over again in order to get statistically reliable results suggests that cutting CO2 emissions could slow the rate of warming as early as 2033, but only if they are ended worldwide in 2020.

One reason for the delayed effect of slashing emissions is natural variability in the climate.

Depending on their phase, the warming of greenhouse gases is either masked or compounded by these kinds of natural effects.

As emissions begin to drop, natural variability will also mask any slowdown of global warming that results.

In spite of all this, mitigating emissions remains crucial to the stability of the global climate and the only way of meeting the Paris Agreement targets of limiting global warming to 1.5-2°C.

Instead, direct measurements of the concentrations of greenhouse gases in the atmosphere may be better, as they will remove the confounding effect of natural variability.