Index
Characterizing Climate Change: It Takes Two Kinds of Number
18 November 2025
Peter Coffee
To grasp the impact of climate change, we have to use two kinds of number – but only one kind of math, just simple arithmetic.
The first kind of number is measures of scale: area of Amazon rainforest, volume of Greenland ice, mass of our planet’s oceans. These numbers tend to be big.
The second kind is measures of rate: tons per year of greenhouse gas emissions, meters per year of glacier recession, hectares per year (or football fields per second) of planet-wide deforestation. These trends versus time may not seem as big as the measures of planetary scale, but there’s often multiplication to follow – with results that get big in a hurry.
A simple calculation that puts climate change in perspective, for me, is the math of Greenland’s ice sheet. It’s not easy to visualize this, but that ice is almost two miles deep at the thickest point – with an average thickness of roughly a mile, and this is over an area of about 660 thousand square miles. In round numbers, we’re talking about 700 thousand cubic miles of ice. Divide that by 140 million square miles of ocean, and we get a value of 0.005 miles of potential sea-level rise if the whole thing melts – because, unlike a melting iceberg that was already floating in the ocean, a Greenland’s worth of melting ice would be new water coming in. (Note also that this would be fresh water, and someday we’ll talk about why that matters.)
Meanwhile, if 0.005 miles of sea-level rise doesn’t sound like a lot, perhaps it sounds bigger in units of everyday weather reporting: that’s more than 26 feet. That’s about the same as the largest storm surge ever recorded in the United States, the 27.5 feet in Pass Christian, Mississippi during Hurricane Katrina in 2005. There is, however, an important difference between ice melt and storm surge: we would now be talking about something that is (i) worldwide and (ii) lasting longer than just a few hours or days. I try not to use the word “permanent,” but this might qualify.
I don’t want to weaken the case by seeming to exaggerate, so I’ll note that no one is currently talking about this happening in less than several hundred years – but that’s not a “never mind,” because the last several years have mostly seen the surprising data and unexpected interactions pushing things in the wrong direction. The most direct causative factors, like global average temperature, keep growing. To put this in simple and tangible terms, the surface of that Greenland ice was 95 per cent liquid in the summer of 2019 – compared to an average of only 64 per cent during the period from 1981 to 2010. Seriously, it’s melting.
Further, if we want to do a little more math, then high-school physics might add some further urgency: yesterday’s warming of the ice sheet’s surface turns into a “warm front,” so to speak, that diffuses downward today and tomorrow – which can’t be stopped, no matter what we do at the surface. If we flipped a switch and went back to 1900s levels of greenhouse gas emissions tomorrow, that heat would still be on its way down to the bottom – and when it gets there, some ice may start sliding on its new underfilm of water. Complications to follow.
I opened this with “two kinds of number,” and there are also two kinds of problem:
There are problems that can be solved when they are seen: get a headache, take an aspirin.
There are other problems that have to be attacked more proactively: cancer is treated as soon as it’s detected, even if it’s not yet causing discomfort. This is why I have a problem with statements like what Bill Gates shared last month, when he said that “Every effort in the world’s climate agenda should…be prioritized by its ability to save and improve lives cost-effectively.” That sounds to me like “fix today’s headaches, the cancer can wait.”
Climate change is like cancer. We know it’s happening. Visible symptoms and simple math. Like the photons that left Proxima Centauri in August of 2021, which are going to get here sometime today, it’s a future that in a sense has already happened even if we can’t yet see it – but we need to believe it.