Sunday, 18 January 2015

Predicting Climate Change is not the same as a Weather Forecast

The chaotic nature of weather makes it unpredictable beyond a few days. 

To predict the weather you need to know exactly what is happening in the atmosphere down to the smallest scale. 

Climate is the average weather pattern of a region over many years (usually a period of 30 years).

Weather forecasts depend on knowing exactly what is going on in the atmosphere, down to the smallest scales. 

Climate forecasts look for patterns over a longer time. 

Will it be generally wetter in winter? 

Will there be more heavy downpours?

A paper published in the journal Science in August 1981 made several projections regarding future climate change.

As it turns out, the authors’  projections have proven to be rather accurate — and their future is now our present.

"Potential effects on climate in the 21st century include the creation of drought-prone regions in North America and central Asia as part of a shifting of climate zones, erosion of the West Antarctic ice sheet with a consequent worldwide rise in sea level, and opening of the fabled Northwest Passage.”

Their predictions have turned out to be correct.

"Drought-prone regions" are receiving less rainfall.

The Antarctic ice has begun to crack and crumble.

Some ships are using the Northwest Passage as a polar short-cut. 

Projecting changes in climate due to changes in atmospheric composition or other factors is easier than predicting the weather.

It is impossible to predict the age at which any particular man will die, but we can say with high confidence what the average age of death for men is.

Similarly, a climate prediction might say that average summer rainfall over London is predicted to be 50% less by the 2080s.

It will not predict that it will be raining in London on the morning of 23rd August 2089.

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