2.12.2014

Define Global Warming and Climate Change

A long time ago, I wrote a post about global warming and climate change.

How do you define global warming and what is the definition of climate change?

When I give it more than 30 seconds of thought, I generally conclude that they are not the same thing, even though they are used interchangeably in the mainstream media (which, incidentally, sucks).

Global warming seems to be defined as an increase in the overall average temperature of the earth. So, for example, if you could measure the temperature at every point on the earth throughout the year (and, to be sure, that would be a formidable task…and how far up into the atmosphere do you measure?), and take an average, you would say the globe is warming if that average temperature goes up from year to year. Scientists don’t measure every point on the earth, but they measure a lot of points and do a statistical analysis to extrapolate to the entire globe (math doesn’t lie, but statistics allows it to wiggle a little bit around the truth…).


Climate change is a more elaborate concept. It has to do with average patterns of weather and ecosystems and hydrology and a bunch of factors that all factor into what are the consistent patterns of climate in a given area. One cannot say the earth has an average climate, the way you could say it has an average temperature. Climates vary from place to place.

However, global average temperature is one factor that affects climate, due to the way the atmosphere and the jet stream are affected by temperature. For example, this so-called polar vortex is the result of more warming in the arctic, which pushes the jet stream further south in winter. The jet stream thus carries more of the still blistering cold (on average) weather down into temperate areas.

Warmer air also holds more moisture. Water vapor is itself a greenhouse gas, so when the atmosphere holds more water vapor, it creates a positive feedback loop of more warming. Also, warmer air masses holding more water vapor tend to cause more rainfall and storms and flooding when they slam into colder air masses to the north. That is what weather fronts are (again, different from climate, but linked to it). So you see more extreme storms and more frequently when the global average temperature rises.

In conclusion, it seems to me that global warming and climate change are different things and that global warming probably drives climate change in ways you would not expect, such as colder winters in the United States, due to a more southerly blowing jet stream. Global warming deniers make the argument, wrongly, that record cold winters prove there is no global warming. But they are actually talking about climate change, not global warming.

This winter has seen some historically cold temperatures in the northern hemisphere. But Australia, in the southern hemisphere, is having record heat waves and drought. The southern hemisphere’s heat is averaging out the northern hemisphere’s cold, and even though we are seeing weather extremes, the average global temperature is rising little by little. But climate is being affected a lot.

That’s why I think it is safe to say that global warming and climate change are different things. A little bit of warming in the average global temperature can really mess things up on a much larger scale when talking about climate.

It’s not rocket science. But it is also not intuitive if you don’t spend a few minutes thinking about it. Thinking is very important. That is the moral of this blog post.

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