There is an important and often misunderstood distinction between weather and climate.
Weather is what is happening when you go outside. It is what meteorologists study and consists of dynamical systems that are highly sensitive to initial conditions driven by the movements of blocks of hot and cold air. It is measured hour by hour (or even minute by minute) and predicted a few days in advance, beyond which the complexities and sensitivities of the system make computational estimation almost impossible.
Climate refers to long term patterns of weather. It is what climatologists study and consists of dynamical systems driven by long term fluctuations in solar activity, oceanic currents, surface albedo and atmospheric chemistry (and, over the very long term, by geological forces and plate tectonics). It is measured in decades, centuries and millennia and predicted in decades.
Predicting the climate
Yet this raises a common question: if we can't predict next weekend's weather, how can we predict the climate in 2050? Remember that climate prediction doesn't mean a prediction of weather, on which day it might rain or be a certain temperature at a given location. It means predicting the overall pattern, which, while chaotic from week to week, fluctuates within a certain range over the long term. Climate prediction means predicting changes in that range within which weather might fluctuate.
Imagine a pot of water being brought to the boil. Although predicting exactly where and when a bubble will appear is almost impossible, it is still quite possible (given knowledge of the original temperature and volume of the water and the amount of heat energy being applied) to predict when it boil with some degree of accuracy. Or consider tossing a coin one thousand times. It is almost impossible to know whether any given toss will be heads or tails, but we can all predict that there will be about five hundred of each. Or think of sitting on a packed train. You mightn't be able to guess how the person next to you is likely to vote in an election, but with knowledge of quality polling data (if that is not an oxymoron), you can make a pretty good estimate of the likely distribution of votes on the train as a whole.
So climate and weather are closely related, but it is important to keep their distinction in mind. One way of putting it I heard recently is that climate trains the boxer, the weather throws the punches.
This distinction means that it is not possible to directly attribute any particular example of weather either to anthropogenic climate change or to natural variation. A cold day doesn't disprove the theory any more than a hot day proves it. Each are a tiny piece of evidence in a much, much larger pattern. And when an extreme weather event comes along (such as the current
Russian heat wave and Asian floods), this too doesn't by itself prove anything. What does count, however, is the
well-recorded pattern of increasing frequency and intensity of such events. Put simply, climate change doesn't cause extreme weather, but it increases the chances of it happening, and increases the extremity of what is possible. This is because warmer air can hold more water, bringing more intense precipitation. By the way, this includes more intense snowfall if the temperature happens to be below freezing, as was seen in the
northeastern US earlier in the year. Or as NASA says, this is
what global warming looks like.
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