How can we depend on computer models of global warming?

Question

When computer models can't even reliably predict the weather 3 days in the future?

Answer 1

For starters, weather is much more unpredictable than climate.  Climate is just the long-term average of weather over the entire planet.  All the little unpredictable variations average out.  Plus meteorologists have gotten pretty good at predicting the weather several days in advance.

We know we can depend on computer models for global warming because they've proven themselves to be accurate.  For starters, they accurately hindcast the temperature changes over the past century:

http://www.globalwarmingart.com/wiki/Ima...

And they've also been used for 20 years now, and have predicted the ensuing warming to a high degree of accuracy:

http://www.realclimate.org/index.php/arc...

http://www.realclimate.org/index.php/arc...

In short, we can depend on computer models because they have proven themselves to be accurate.

Answer 2

We know (without computer models):

1) Climate (average of weather over 30 years) is warming

2) Greenhouse gas levels are rising

3) Increase in greenhouse gas is coming from human activities

4) Greenhouse gases hold heat, that would escape to space, near the planets surface

5) Increased levels of greenhouse gases will hold more heat, warming the planet.

A simple math equation (no computer required) using well established physics can show that as greenhouse gas levels continue to rise (all other things remaining equal), the planet will warm.

The uncertainty lies in how much various feedback effects will warm or cool the planet. That's where computer models are the only tool scientists have. And while they aren't perfect, that doesn't mean they are useless.

Answer 3

well their so complicated that we can change a few factors to make it seem the way we want to. If a scientist made a computer model predicting minor fluctuations in 50 years time and it doesn't lead to anything caterstrofic then noone would have any interest in it. On the other hand if he made a model prediciting absaloute terror and apocalypic cercumstances then he'll recieve a much better response from the media and other bodies of society.

Answer 4

Well, all models are subject to error, but you can learn a lot from them.  Here's a couple of reasons to trust them:

1. The idea is not to predict the weather 50 years from now, it's to predict the average climate then.  That's something completely different.  When you say models can't reliably predict weather 3 days in advance, it's often because the weather pattern is slightly different than what was forecast: faster, slower, farther north or south.  It may have gotten the weather "right," but slightly misplaced in time or location.  Those sorts of errors may average out when run over the time periods of global climate models.  So even though they may not be able to predict the weather then, they can accurately predict how much rain will occur or what the temperature will be when averaged over a year. That's what climate models are intended to do.

2.  They verify the models by running them against the past.  We know what the climate of the past century was like, so we can start with conditions of a hundred years ago, the ocean temperatures, the amount of ice at the poles, the amount of carbon dioxide in the atmosphere, etc., and then run the model forward in time and see if it matches up against what actually happened.  If it did, great; if not, back to the drawing board.

But look, they're never going to be perfect, but if they all say that something dire is going to happen, maybe we should pay attention.  We have a solid physical background to expect warming, and if they show that, we shouldn't be surprised or try to deny it.  

I think their biggest problem will be that they won't accurately model what quantity of fossil fuels are actually still available.

Answer 5

You can't.  Even when you read most of the reports of those scientists who are proponents you will see that they have qualifying paragraphs that make for interesting reading.  They leave plenty of room for doubt.

Many of the reports come right out and say something to the effect that sun cycles, la nino and la nina and other factors also impact the global climactic cycles and that the researchers do not have full understanding of how those factor into their models.

If you want to do something interesting research the properties of steel over different conditions of temperature and stress and minor metalurgical differences.  Under real world conditions of temperature and different types of torque, impact and straight pressure, steel can vary from almost rubbery to brittle.  

In our world we like to think of things as being linear and that we can extend something from a lab out to infinity in a straight line.  Or we like to think that all things can use a formula to approximate them.  The truth is often times a formula will approximate something for only a limited set of conditions and when you extend it out the formula breaks down - sometimes drastically.  For example a portion of a bell curve is very linear and a linear formula can be used for that portion and it would model that portion of the curve very well, because that portion is very close to linear.  But when you extend it out you find that the formula is not even close to approximating the total bell curve.

Some researchers who want to find for AGW like to ignore and minimize what they consider are minor extraneous factors, I personally believe it is like minor changes in the metalurgical composition of steel.   What appear to be minor changes can have a major impact in the real world.

Answer 6

There are many different computer models of man-made global warming, all of which were programed with selected data, and NOTHING that they have predicted has occurred.

Myself, I'm more worried about ManBearPig destroying the economy of the free world.

Answer 7

I don't know if you fly much but airplanes and most machinery that costs c**p tons to build are first "built" and tested with computer models to make sure they'll work correctly.  That obviously works reasonably well.  So don't just throw out computer modeling in general.

We cannot predict weather patterns very far in advance because our weather is a chaotic system where small changes in what our initial conditions are lead to exponential changes down the road.  That is, we can only measure the best estimates of the data we have of the current conditions so finely and there will always be errors made.  Those errors then produce significant changes down the line as to what actually happens vs what our best estimates say would have suggested.

However, if you take a range of values around what our best estimates are, and follow those through and they all lead to the same qualitative result, then it isn't unreasonable that that result will eventually take place.  In weather predictions we are concerned with precisely where a rain storm occurs, but we can predict that SOMEWHERE a rainstorm will occur fairly accurately.  That kind of qualitative predictions ("that" something occurs as opposed to "where" something occurs) is more along the lines of global warming models.  And that is something we can do very well.

EDIT:  I'm not the standard moron that answers questions on here and I actually know what I'm talking about.  I'd really love to know who gave me the thumbs down and what their educational background is.

Answer 8

hah, good question.

Answer 9

You can't. NOAA is groping in the dark. The 30 year difference in the 2006 & 2007 projected & actual melting rates could be your first indication. We're living within a self equalizing chemical system driven by heat from our Sun. When something does change, the change will start off very slowly. Then almost overnight, the rate of change per day increases significantly. This is due to the fact that mathematically the primary value that controls the slope of the change curve over time, is an exponent.