Why we have seasons
This Thanksgiving I am grateful for many things, and I count critical thinking skills and basic science literacy as part of that collection. Around this time of year, it is common to see people say things like, “They don’t seem to talk about global warming during winter” or “If there is climate change, why is it snowing today in Boston?” It should probably not be surprising because there are probably people who believe Greenland is, well, green or that it only gets hot in deserts. Here’s why the season of winter does not disprove global warming, climate change, or whatever you want to call it.
Our climate is changing through a combination of natural variability and a human-caused steroid, anthropogenic activities, on top of it. Increasing greenhouse gases, changing landcover, and growing population demand have modified the climate in such a way that weather, sea levels, the water cycle, agricultural productivity, infrastructure, and much more are being impacted. Even with all of that clearly established, fundamental science explains why we will always have winter even as climate warming continues.
The seasons are caused by the fact that our planet is tilted on an axis roughly 23.5 degrees (graphic above). According to the Library of Congress website, “Many people believe that the temperature changes because the Earth is closer to the sun in summer and farther from the sun in winter…the Earth is farthest from the sun in July and is closest to the sun in January!” So what’s going on? During the summer when the Earth is tilted towards the sun, the energy is more directly focused on the Earth. In winter, energy is more spread out. It is similar to shining a flashlight directly down on a table or at an angle. The beam is broader when the flashlight is at an angle (winter). The Library of Congress website goes on to say that during winter, “….The long nights and short days prevent the Earth from warming up. Thus, we have winter!”
Carbon dioxide in the atmosphere over the past 800,000 years. The dot at 414.7 pm represents 2021 … [+]
By the way, the axial tilt of the planet and changes in the way the Earth orbits around the sun are responsible for many aspects of the naturally-varying climate like glacial (ice ages) and interglacial periods. Look carefully at the graphic above. You can see the naturally-varying cycle associated with these Milankovich Cycles. Now look at the carbon dioxide levels (the dot in the upper right corner) at year 0 (roughly the present). It is well beyond the naturally-varying cycle over the past 800,000 years. This graph illustrates the “and” aspects of climate change not the “or” aspects. In other words, natural variability happens and fossil fuel burning after the Industrial Revolution is accelerating climate change.
It is important to remember that even in 2040 or 2080 when our climate could even be warmer than now, there will still be winter. It will still snow in Boston. Cold snaps will happen. The polar vortex will even still be around. Even as I write these facts, the fingerprint of climate warming is apparent in winter changes. According to an analysis by Climate Central, over 200 weather stations experienced shrinking winter cold snaps during the period 1970 to 2021. Cold snaps decreased by roughly 6 days on average since 1970.
A study in the journal Science found that enhanced warming in the Arctic is causing more stratospheric polar vortex disruptions, which could lead to extreme cold events like we saw in Texas. Some scientists have even suggested that blizzards could become more extreme due to climate change. For many people, these things seem counterintuitive. The atmosphere and the Earth system are complex systems. Many things that happen do not fit our mental models. That, however, does not mean they are hoaxes.
