As the Eaton and Palisades fires continue to burn past the more than 38,000 acres they’ve already consumed, the time is right for a conversation about what led up to this disaster.In the short term, displaced homeowners and renters allege Southern California Edison failed to de-energize its electrical equipment despite weather service warnings about 100 mph wind gusts and extreme fire risks. Bigger picture, scientists know that the fire risks have been decades in the making. UC Riverside climate scientist Francesca Hopkins explains how carbon emissions from human activities turn into conflagrations. Hopkins runs the Greenhouse Gas Emissions Lab at UCR, and she has some ideas about making urban landscapes more resilient.
Francesca Hopkins, associate professor of climate change and sustainability.Q: There are many who understand climate change is making all weather events more extreme, including fires. Can you offer a little more detail about the mechanics of these changes?A: All of this is related to a phrase coined by Daniel Swain, a climate scientist with UC Agriculture and Natural Resources. The phrase is “hydro-climate whiplash.” This refers to a climate with extreme high precipitation events in winter, followed by abnormally intense droughts.As a direct result of greenhouse gas emissions from human activities, the atmosphere is warmer than it used to be. Greenhouse gases like carbon dioxide or methane create something like a blanket in the atmosphere, trapping heat from Earth’s surface and preventing it from radiating out into space. This makes the planet warmer. As the atmosphere gets warmer, it can hold more water vapor. It’s a better sponge than it was before because of the extra warmth. Why is that? There’s a relationship between temperature and the amount of water vapor the air can hold, called the Clausius-Clapeyron relation.This is an equation that describes a relationship that is exponential, rather than linear. It describes an increase in the specific humidity, or the amount of water vapor a given mass of air can hold, with temperature. In other words, there is a much larger mass of water in the air than there was before.Specific humidity isn’t like the relative humidity we feel when we go outside on a sticky day. But it is something we understand intuitively when there’s heating or cooling of air. For example, fog forms when it gets cold at night and the air cools rapidly, forming water droplets as the air is less able to hold on to the water that was a gas during the day.The atmosphere pulls water out of things that lose it, like plants and soil. And, if you have enough water to create a precipitation event, there will be more rain coming down because there’s more water in a warmer atmosphere. In Southern California, we had two really wet winters, 2023 and 2024. Since plant growth is limited by the amount of water available, that gave us a lot of extra plant biomass. But we haven’t had rain in eight months, s
