Next Generation Science Standards:
- MS-ESS3-5: Ask questions to clarify evidence of the factors that have caused the rise in global temperatures over the past century
Key Vocabulary: temperature, average, axis, tilt, hemisphere, orbit, season
It’s been cold. Really freaking cold. I live in Ohio, and like most places in the United States, we have been experiencing dangerously frigid temperatures the past few weeks. With record lows being registered across the country and spring still several months away, you may see certain ideologues take to social media explaining that the recent snowy, icy days disproves years of scientific climate research. You might even see an elected official throw snowballs around the US Capitol, proving the planet could not possibly be warming if there is snow on the ground.
However, cold weather in one part of the world does not mean the overall climate is not changing. While North America is currently experiencing temperatures much colder than average, other parts of the world are observing the opposite. Indeed, while most of the continental U.S. has plunged into a deep freeze, the Earth as a whole is currently about a 0.9°F (0.5°C) warmer than the historical average for this time of year. The Arctic has recorded daily highs that are over 5°F (2.9°C) above average, which could further damage an already at-risk ecosystem.
Why is winter cold?
We experience winter, and all seasons for that matter, because the Earth rotates at an angle titled to its plane of rotation. This tilt, called obliquity, means that as the Earth orbits the Sun, the hemisphere that is pointed towards the Sun changes.
Between late September and late March, the Northern Hemisphere is angled away from the Sun. This means that the Sun’s energy hits that part of the Earth much less directly, resulting in (generally) colder temperatures in that hemisphere. The closer you are to the pole, the less direct sunlight you will receive. As such, the further North you go, the (generally) colder your winter will be.
At the same time, the Southern Hemisphere is angled towards the Sun, exposing it to more direct energy, and causing (generally) warmer temperatures. While the Northern Hemisphere experiences cold weather and little daylight, those who live south of the equator enjoy long, warm days.
But as the Earth continues on its orbit, the side that is tilted towards the Sun changes. In a few months, the Northern Hemisphere will be angled toward the Sun, meaning more direct sunlight, warmer temperatures, and the season of summer. This excellent interactive illustrates the tilt of the Earth and how sunlight is distributed as it moves around the Sun (click “continue to interactive” in the top right corner to play).
Cold days in winter do not prove the climate is not changing; since the Northern Hemisphere is currently angled away from the Sun, we would expect to see colder days. Experiencing frigid temperatures while the hemisphere where you live is facing away from the Sun is not indicative of the overall climate. It’s the result of our Earth being a bit lopsided as it orbits the Sun and solar energy being distributed disproportionately across the globe. Just because it’s winter where you live right now doesn’t mean the Earth’s average temperature isn’t increasing.
However, the Earth is a complicated system, and there are more factors that affect the climate that just the tilt of the axis. Air and ocean currents play a critical role in distributing heat energy around the planet. The Gulf Stream carries warm water from the Caribbean all the way to Northern Europe, causing their winters to be more temperate than would be expected given its latitudes. Water also retains heat longer than air, which usually keeps the coast warmer than the interior of the continents.
There’s also atmospheric composition, which if altered, could change how the Sun’s energy is absorbed by the Earth. Scientists have extensively linked increasing carbon dioxide levels in the atmosphere due to the burning of fossil fuels to increasing global temperatures. We take a closer look at climate data in Part 2.