What affects our climate?
Adapted from "Climate" from Khan Academy and "The Greenhouse Effect and Climate Change" from General Biology by OpenStax.
In general, temperatures on Earth’s surface drop as we move from the equator to the poles. The equator gets more insolation, or solar energy per area per time, than the poles do. Rays of sunlight hit the Earth directly near the equator, but at an angle near the poles, so the same amount of energy is spread over more area in the polar regions, as you can see in the diagram shown to the right. Also, at the poles, sunlight travels a longer path through the atmosphere before reaching the surface. That means more light is deflected into space by particles in the atmosphere (and thus never reaches the surface) at the poles than at the equator.
The strong sunlight at the equator (and weak sunlight at the poles) makes the tropics warmer than the Arctic. Not only that, but this difference in solar input also generates major global patterns of air circulation. Because air is heated by the sun most strongly at the equator, it has the greatest tendency to rise there. This rising of air at the equator drives large-scale patterns of air flow and rainfall. What do these large-scale patterns look like? Earth's atmosphere contains six rotating cells of air are found (three north of the equator, three south of the equator). Each of these cells encircles the Earth like a giant "air donut," as shown in the figure to the right.
In this six-celled pattern of air flow, air rises in low-pressure zones - one at the equator and two more at 60° N and S. As it rises, the air cools and drops much of its moisture as rain or snow. This leads to regions of high precipitation (rain or snowfall) at the equator and at 60° N and S.
Having already dropped its moisture, the air that rose in the low-pressure zones is dry as it flows towards the poles (traveling high up in the atmosphere). When it comes down again in high-pressure zones (which are found at 30° N and S and at the poles), the dry air sucks up moisture from the surface, resulting in bands of desert at 30° N and S and in dry regions at the north and south poles.
Earth is also surrounded by an atmosphere that contains greenhouse gases (GHGs). These gases allow visible light from the sun to pass through, but block some of the heat energy radiating off Earth towards space. In this way, they help trap heat energy that subsequently raises air temperature. Being a greenhouse gas is a physical property of certain types of gases; their molecular structure allows them to absorb wavelengths of infrared radiation, but remain transparent to visible light. Some notable greenhouse gases are water vapor (H2O), carbon dioxide (CO2), and methane (CH4). GHGs act like a blanket, making Earth significantly warmer than it would otherwise be. Scientists estimate that average temperature on Earth would be -18º C without naturally-occurring GHGs.
Elevation above sea level is another key factor that shapes an area's climate. Places at high elevations tend to have a colder climate than nearby low-lying areas. Because temperature changes with altitude (along with things like moisture and soil type), a mountain can have different biomes at different altitudes. For instance, a tall mountain may have grassland on its lower slopes, but a zone of alpine tundra, like the arctic tundra biome found near the north pole, at higher elevations.
Mountains also affect patterns of rainfall, both on their own slopes and in surrounding areas. Imagine the case where a mountain tends to get hit by winds coming from a certain direction—say, off the ocean. Especially if those winds are damp, the windward (wind-facing) slopes and surrounding areas will tend to get lots of rain.
Why is that the case? The air loses its capacity to hold water as it rises and cools while moving up the slopes, and it drops the extra moisture as rain. The air that makes it over the mountain is dry, so the other side (the leeward side) tends to have a desert-like climate. This dry region on the leeward side is known as a rain shadow.
Another important factor that affects an area's climate are bodies of water, especially larger ones like oceans or lakes. At a basic level, lakes, oceans, and streams play a vital role in climate processes by serving as reservoirs for water, which can evaporate from the surface to fall later as rain or snow. Bodies of water also minimize changes in temperature of nearby landmasses. That is, they keep high temperatures from getting as high and low temperatures from getting as low as they otherwise would.
Finally, ocean currents (which carry water from one place to another) can strongly affect the climate of nearby land. The map on the right shows some of Earth's major currents. (Red = warm currents, blue = cold currents, black = neutral currents)
Take a look at the Gulf Stream, for example. The Gulf Stream is a current that carries water at the equator up past the eastern coast of the United States, feeding into another current called the North Atlantic Drift. As a result, two cities at the exact same latitude, one in England and one in Canada, may have very different climates. The city in England might only barely reach freezing temperatures during winter, while the city in Canada may spend most of winter at below zero temperatures - ocean currents can have a very significant effect!
