For more than a century, scientists have taken temperature readings around the world from land-based labs, ships, and satellites. These historical temperature records show that the Earth is warming, and that temperatures are rising the most in large land masses and areas near the earth's poles.
"Our observations tell us this, but it also fits right in with the laws of physics and our expectations for what would happen," says Adam Schlosser, the deputy director at MIT's Joint Program on the Science and Policy of Global Change.
One thing physics tells us is that water reflects much of the sun’s energy back into the atmosphere, while a land mass absorbs much more of that energy. That means it takes more added heat to raise ocean temperatures than land temperatures. This is why most of the warming we see today is happening on continents rather than over the ocean.
This is true of all land on Earth, but the effect is even stronger near the poles. Here, rising temperatures have melted large amounts of snow and ice—white surfaces that normally reflect the sun's rays back into the atmosphere and keep the areas they cover cool.
"The snow ice surfaces have a very high reflectivity," says Schlosser. "And as you eat away at that, the underlying surface absorbs a lot more energy than it would have otherwise."
There are other, less significant, reasons the poles are warming faster than other parts of the planet, including changes in ocean circulation (1). Other possible contributors, like shifts in cloud patterns, are still being studied (2).
The physics behind these global warming patterns can also apply to smaller, local regions. High altitude regions that normally have a lot of snowfall may warm faster as they lose their reflective blankets of snow. Atmospheric changes to wind patterns and cloud cover have also caused the Middle East, northern Asia and parts of Europe to warm faster than the planet as a whole (3).
Many of these local warming trends are still poorly understood. Temperature records can tell us which parts of the Earth are warming fastest, but not why, or whether these warming patterns will hold as the climate continues to change. To study these questions, scientists rely on climate models, which are continually being refined.
Still, in the big picture, we can be confident that the continents will continue to warm faster than the oceans. And this has major implications for human societies.
"Just about every human lives on a large land region," says Schlosser. "This means that almost everybody will experience a stronger warming than what the global climate talks suggest when they reference global warming averages of 1.5 or 2 degrees Celsius. And this has impacts beyond ourselves: it has major implications for our food, water and resource systems."
Published August 17, 2021.
1 Clem, Kyle R., et al. "Record warming at the South Pole during the past three decades." Nature Climate Change, 10, 2020, doi:10.1038/s41558-020-0815-z
2 Alkama, Ramdane, et al. "Clouds damp the radiative impacts of polar sea ice loss." The Cryosphere, 14, 2020, doi:10.5194/tc-14-2673-2020
3 As shown in historical temperature datasets compiled by the NASA GISS Surface Temperature Analysis, the NOAA Merged Land Ocean Global Surface Temperature Analysis, and Berkeley Earth.