Myles Allen

In the 1990s, scientists detected a human, quote, "fingerprint" in the Earth's atmosphere, a distinctive pattern that differs from warming caused by changes in the Earth's orbit or the sun's output.

But whose fingerprint is it? Are all of us responsible, or are some of us more responsible than others? The British climate scientist Myles Allen asked himself those questions as he watched the Thames River rise outside his house after an epic rainstorm in 2003.

In an article he later wrote for the journal Nature, Mr. Allen asked, "Will it ever be possible to sue anyone for damaging the climate?" His answer: Given the rapid advances of science, maybe soon.

Mr. Allen's reasoning was straightforward.

Fossil fuel companies sell oil, gas, and coal that, when burned, heat up the atmosphere, which increases the likelihood and severity of events like the flood that had threatened to swallow his house.

Mr. Allen knew that climate scientists could do the math.

Basically, they plug all the data for an extreme weather event such as a flood or a heat wave into a climate model and run it.

Then they lower the carbon dioxide level in the model, creating a counterfactual world without human influence in the Earth's atmosphere, and estimate the probability of the event.