Human-driven climate change has quadrupled the frequency of coastal sea level extremes since 1900, according to research published in Nature Climate Change. Research published in Nature Climate Change found that once-in-a-century flooding events now strike on our planet about once a decade. A separate study published in Science Advances found human-caused sea level rise was measurable at 97% of sites sampled around the world, and was responsible for around 58% of the observed daily extreme water level exceedances between 2000 and 2018.
The changes are happening much quicker in low-latitude locations. The reason is that in the tropics you typically have a less variable climate. For those living in low-latitude tropical regions, the impact is more severe than in regions like the North Sea, where infrastructure is adapted to massive changes of multiple meters.
In Plain English: The Takeaway
- Frequency Shift: Floods that used to happen once every 100 years are now happening every 10 years on average.
- Inevitability: If you look into projections, they all agree with respect to what happens until around 2060, independently of how much greenhouse gases are emitted.
The Mechanism of Anthropogenic Forcing and Sea Level Extremes
To understand why this is happening, we must look at anthropogenic forcing—the influence of human activity, primarily greenhouse gas emissions, on the Earth’s climate system. Researchers used climate models to isolate this effect by keeping greenhouse gases constant in simulations to see what natural variability would produce. The result showed that since the 1970s, human activity has become the dominant driver of sea level extremes.
These extremes include storm surges, high tides and rising sea level anomalies. A separate study in Science Advances confirmed that human-caused sea level rise was measurable at 97% of sampled sites globally and accounted for approximately 58% of daily extreme water level exceedances between 2000 and 2018. As the baseline sea level rises, the “hurdle” for a storm surge to cause flooding is lowered.
Impact: From Infrastructure to Daily Life
In the United States, Sönke Dangendorf noted that in places like Norfolk, Virginia, sea level rise means that high tide leads to flooding. You see flooded streets, and that affects your commute. It also makes it very hard for you and your coastal community because you have increasing insurance costs — the accumulated costs of these events can easily be as much as a major hurricane making landfall.
| Metric | 1900 Baseline | Current State | 2050 Projection (IPCC) |
|---|---|---|---|
| Frequency of 100-Year Event | Once per century | Approximately every decade | Annual at 19%–31% of sites |
| Primary Driver | Natural Variability | Anthropogenic Forcing | Committed Sea Level Rise |
The Tropical Sensitivity Gap: Why Geography Matters
Sönke Dangendorf, lead author of the Nature Climate Change study, highlights a stark contrast between the North Sea and tropical regions. In the North Sea, we have a storm season, and we have huge tide ranges. We are already adapted to pretty massive changes of multiple meters, so a couple of centimeters of sea level rise do not play out that hard, but in the tropics, where it’s more calm, it makes a huge difference.
Using a hurdle-runner analogy, the tropical environment is like a runner who consistently jumps just below the hurdle. When the hurdle is lowered, that runner suddenly clears it every single time. This means that the constant jumper is way more sensitive to these changes.
The Path Toward Adaptation
The data suggests we are already “committed” to certain levels of sea level rise through 2060. We need to adapt to that sea level rise, but if we mitigate climate change, if we stop emitting greenhouse gases, then we can avoid dangerous sea level rise, and that’s very important.
References
- Nature Climate Change (Study published June 10)
- Science Advances (Study on human-caused sea level rise)
- Intergovernmental Panel on Climate Change (IPCC) Reports
