How can predicting the future climate become more complicated than simply extrapolating from past records?

Answer 1

Global climate dynamics can't be reduced to a linear function.

In order to predict the future you must not only know where you were but how you got there in the first place. Believe it or not, we don't have everything about climate figured out. Closer than years ago, yes, but like most sciences, it's a matter of "the more we know, the more we realize we don't know."

Answer 2

It's a good question and one that makes a lot of sense.

Predicting the future climate means predicting what the climate will do of it's own accord and then factoring in how human activity is going to have an effect. There are a great many variables related to both these aspects.

If we wind the clock back to a time before humans were affecting the climate we can see that the climate is never constant. In the last 1000 years for example there have been a couple of notable anomolies, first when the world warmed up approx 800 years ago and then when it cooled down approx 400 years ago. We know why these events occurred but the causes at the time were largely unpredictable.

A greater understanding of the cycles that Earth and the Sun go through mean we can accurately predict the known variables but there are unknowns that we can only really guess at.

Because there are no overall constants and many variables it means any extrapolation is subject to a level of variance, this is one of the reasons that no climatologist will say the world will warm up by X number of degrees but instead will apply a range saying the world is expected to warm by between X and Y degrees.

The human element is in some ways more predictable. We can accurately measure how much greenhouse gases we are adding to the atmosphere, we know how much each of the different gases contributes to global warming (some are much more effective than others) and this allows us to calculate accurately what would happen if we added X tons of carbon dioxide, Y tons of methane and Z tons of nitrous oxide for example.

What we don't know of course is just how much of these different gases we'll be releasing in the future. As technology progresses there will be applications that reduce emissions but conversely there will be applications that increase emissions. We can assign projected values and work out accurate calculations but these calculations are only accurate if the assigned values transpire to be correct. Again, the values used fall into a range.

So, we have variability in both the natural and human component of future predictions, the two compound each other and give rise to a range of predictions. As in any similar situiation, it's best to look at ranges, means, medians and modes and extrapolate from there.

If we look at the eight models used to predict the climate by the turn of the century and incorporated into the Special Report on Emmission Scenarios (SRES) commissioned by the IPCC for the Third Assessment Report (TAR) then the range is 1.4 to 5.8°C, there's two modes at 2.2 and 3.8°C, and both the median and mean are 3.4°C. Other than the modes at 2.2 this is a nicely balanced group of numbers showing a good degree of consistency. It would therefore be reasonable to suggest that with 100 years the world will probably be 3 to 4°C warmer than it is now.

Answer 3

Predicting the future is more difficult because we don't know what's going to happen in the future. For example, we could reduce the worldwide greenhouse gas emissions by 80%, or they could increase by 80%. That's why climate modellers make a range of possible future results depending on the changes in our greenhouse gas emissions.

The IPCC report predicts that the planet will warm something like 1.8-5.6°C over the next century. The 1.8 is if we make a big reduction in greenhouse gas emissions, the 5.6 is if they continue to increase. However, the 5.6 doesn't take into account many feedbacks such as the oceans emitting more carbon as they warm up (because CO2 is less soluble in hotter water). They don't include these effects because they're very complicated and it's hard to know at what point they'll kick in, but some models have predicted that we could get as much as 11°C hotter in the next century. That's sort of a worst case scenario that almost certainly won't happen, but you can see why it's so difficult to model the future climate.

Answer 4

Crunch all the past weather data for as long as we have records, and you still won't be able to accurately predict if it will rain in Spain on the plain tomorrow.

Whoever says they can accurately "model" what the climate will be in 100 years, or 10, or one.... is a fool or a liar.

Answer 5

You are suggesting extrapolating assumes all conditions remain the same, they don't. You must make assumptions regarding the best and worst case scenarios and accept that your answer lies somewhere between those two extremes.

Answer 6

When man starts dumping huge amounts of greenhouse gases into the air, that changes things.

http://www.globalwarmingart.com/wiki/Image:Climate_Change_Attribution.png

Mind you, it makes predicting climate real easy. No matter what, long term climate is going to get warmer.

Answer 7

Past records only go back less than 200 years. That data doesn't show global warming. In order to advocate global warming, you have to perform elaborate calculations on ice cores and tree rings. These methods are very complicated and controversial.

Answer 8

No one can predict what the future will bring.

Answer 9

From past records that could be in error of + or - 2 deg. F.