2024 will be a year to remember. As a result of fossil fuel-driven climate change, it’s on track to be the warmest year in recorded history. This heat fueled extreme weather events across the world, with most having significant impacts on human life and infrastructure and ecosystems.
In the United States, communities are still recovering from Hurricanes Beryl, Helene, and Milton. Each storm made history in its own right: Beryl was the earliest Category 5 storm on record in the Atlantic Ocean, Helene broke rainfall records in Georgia, North Carolina, South Carolina, and Tennessee, and destroyed tens of mountain communities, and Milton was the second fastest intensifying storm since 1979. I wrote about the unprecedented Hurricanes Helene and Milton in an earlier blogpost.
In other parts of the world, floods, heatwaves, wildfires, and droughts made headlines. Flooding in Central Europe this summer killed 27 people, while extreme rains in Pakistan and Afghanistan left hundreds dead and thousands of families homeless. In Brazil, the world’s largest grassland caught fire; a rapid attribution study found the fire to be 40% more intense due to climate change. And in the African Sahel, including countries like Senegal, Mali, and Niger, an extreme heatwave at the end of Ramadan would not have occurred without human-caused climate change.
How exactly does human-caused climate change lead to more frequent and more intense extreme weather events? In this blog, I explain the science behind these extreme weather events and pinpoint how additional heat-trapping emissions in Earth’s atmosphere are responsible.
The Earth is warming
The burning of fossil fuels has led to an increase in pollutants such as carbon dioxide in the atmosphere since the industrial revolution began in the 1800s. Carbon dioxide and other pollutants trap heat in the atmosphere that would otherwise leave the Earth, acting as a sort of blanket that doesn’t allow the Earth to emit as much heat as it used to.
This is fossil fuel-driven climate change—more heat-trapping emissions in the atmosphere results in a warming planet, with a clear warming trend observed over the last few decades (Figure 1).
It didn’t have to be this way—the fossil fuel industry was broadly aware of the danger its products posed to the global climate since at least the mid-1960s, but chose to downplay and distort the evidence of climate change while engaging in a decades-long global campaign against climate action. And now we’re dealing with the consequences: as global warming has progressed, it has also amplified extreme weather events around the world.
Figure 1. The global average surface temperature since 1880. Source: NOAA (https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature)
Droughts and floods are worsening
To understand why droughts and floods are worsening on a warming planet, there’s a concept in atmospheric science called the Clausius-Clapeyron relationship that we’ll need to review (bear with me here, I promise it will help!). It states that the atmosphere can hold 7% more water for every one-degree Celsius increase in temperature.
In my previous blogpost, I explained the Clausius-Clapeyron relationship through an analogy where I envision the atmosphere as a sponge: as the temperature increases, that sponge gets bigger and bigger, allowing the atmosphere to hold more and more water.
How does this affect the frequency and intensity of droughts and floods? If the sponge (atmosphere) can hold more water, it can hold off on raining out (imagine squeezing a sponge) longer. So, one of the reasons droughts are getting worse in some parts of world is due to the atmosphere being able to hold more water before that water leaves the atmosphere. As just one example, climate change is worsening the megadrought in the western U.S.
For the same reason, this “sponge effect” also results in more floods—when the atmosphere finally rains out, it dumps much more rain than it used to in a given period of time. This is one of the reasons why we’re observing unprecedented heatwaves and droughts in the Sahel, while record-breaking flooding is occurring just a few thousand miles away in Pakistan and Afghanistan.
This simple analogy works great when considering the global average change in droughts and floods. However, the change in the frequency and intensity of droughts and floods varies for different regions (Figure 2).
For example, there is a clear increase in heavy precipitation over Europe mainly due to a warmer atmosphere being able to hold more water. Specifically, many regions in Europe will see an increase in rare heavy precipitation events, while only a slight increase in less rare events. Climate change is also causing a “precipitation whiplash” in some cases—abrupt shifts between extreme dry and extreme wet conditions in the same place, including in California.
Figure 2. Observed changes in heavy precipitation (top) and agricultural and ecological drought (bottom). More information can be found in the IPCC’s Summary for Policymakers: https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf.
Storms are breaking records
The atmosphere is warming rapidly, yes, but it’s actually warming slower than it could be thanks to the Earth’s oceans, which are absorbing 92% of the heat from human-caused climate change. However, all this additional heat in the oceans is leading to record-breaking heat content levels, which also result in record-high ocean surface temperatures. According to the Climate Shift Index from Climate Central, record-breaking ocean surface temperatures in the Gulf of Mexico were made 400-800 times more likely due to fossil fuel-driven climate change.
Tropical cyclones such as hurricanes develop in the tropical oceans due to an imbalance in heat between the cool upper atmosphere and the warm ocean surface. If there is a greater imbalance in heat between these two regions, for example, a warmer ocean surface, then the hurricane can strengthen faster and become a more intense storm.
This is exactly what happened this year with Hurricanes Beryl, Helene, and Milton. Beryl reached Category 5 strength so early in the season because it traveled over waters that were significantly warmer than usual due to climate change. Helene and Milton experienced rapid intensification in the Caribbean and Gulf of Mexico, respectively, due to record high heat level content.
In the future, as the world continues to warm due to additional heat-trapping emissions, storms like Beryl, Helene, and Milton will become more common.
COP29, the L&D fund, and climate attribution
In less than two weeks, the world’s governments and organizations will convene at the United Nations Framework Convention on Climate Change’s 29th annual Conference of the Parties (COP29) in Baku, Azerbaijan. The backdrop will be the news of 2024’s unprecedented year of extreme weather fueled by fossil fuel-caused climate change.
At COP29, nations will decide how to fund lower-income countries’ climate adaptation and mitigation needs; my colleague, Rachel Cleetus, nicely lays out what we’ll be following this year at COP29 in this blogpost. These contributions to lower-income countries are critical as extreme weather events worsen in a warming world; we need to be sure that every country has the money necessary to adapt to climate change.
I’ll also be following the discussion on the operationalization of the Loss and Damage fund. L&D is a term that accounts for any loss or damage, economic or non-economic, due to an extreme weather or climate event. As part of my science fellowship with the Union of Concerned Scientists, my goal is to first identify gaps in scientific literature that could help bolster and reinforce the L&D fund, and then apply a machine learning method to fill that research gap.
Specifically, I’m interested in summarizing the current state of climate attribution science, which is a subfield of climate science that basically answers the question, “was this extreme weather or climate event more likely due to climate change?” Currently, we know that there are large gaps in climate attribution literature, for example, a lack of attribution studies in more vulnerable regions—especially in the Global South.
Following the L&D conversation at COP could better clue us climate scientists into what those on the frontlines of the climate crisis need and help us advocate for that at COP.
As we enter an era where years like 2024, with its unprecedented number of extreme weather events, become more common, it is up to the world’s governments at this year’s COP to resist fossil fuel industry lobbying. Governments must signal more ambitious emissions reduction commitments while agreeing on a robust climate finance goal that can, among other priorities, enable further strengthening of the world’s infrastructure to prepare for more extreme weather and climate events.