Climate modeling is actually 'one' of the ways we come to understand climate on earth. That's because we don't have extra planets that are just like earth to experiment on. Some say that models can be wrong. It's a common mistake people make... the point is not that models 'can' be wrong. The point is models are 'always' wrong, that's because models are not real, they are models. But that does not mean that they are not relevant and useful for understanding how things work. The truth is that if you only use measurements and raw data, you can't even get close to the truth about climate.
In science, it is often preferable to do an experiment. But to do an
experiment with global climate, we would need more planets just like
earth to test. Then we could try different mixes of greenhouse gases in
the atmosphere and see what happens. However, since we don't have any extra
planets, we need to model the climate: Experiment: Webster, Wiki
The reality is that raw data is terribly misleading when measuring the earths temperature. Many aberrations need to be compensated for. That means that if you want to get a more accurate picture, you need to model the measurements and correct for aberrations. You make a model and test it. And others test it. And you refine it. And you refine it some more. It will never be perfect, and it can always be improved, especially when dealing with complex systems like climate: Model: Webster, Wiki
An Important Point
Many people falsely assume that models are not perfect therefore we
don't understand climate. This is a misnomer. Models only help us
understand climate in a more reasonable way, they will never be perfect but they do reasonably show us what is happening in the climate of earth.. The actual observations are clear enough at this
point that modeling is not required to understand that the earth is warming. We see the ice melting, the sea level rising and other affects such as seasonal shift, prolonged forest fire seasons, regional drought trends also support the observational confirmations.
Simply put:
We know the amount of GHG's mankind has produced quantitatively.
We know that should produce a relatively certain amount of forcing.
In other words, the anthropogenic signal is strong enough that we are certain this global warming is:
Occurring
Attributable to the forcings caused by human output of greenhouse gases.
Some are still "under the mistaken impression that
concern about global warming is based on climate models, which in
reality play little role in our understanding -- our understanding is
based mainly on how the Earth responded to changes of boundary
conditions in the past and on how it is responding to on-going changes."
- Dr. James Hansen
Climate System Models
General Circulation Models (GCM's)
GCM's are used to understand the forcing systems that influence climate here on earth.
By feeding data into the model simulations, scientists are able to test potentials and evaluate the various influences of the earth climate system.
Just because they are simulations does not mean that they are not useful or accurate. In fact
modeling climate is the only way to estimate climate functions with any
degree of accuracy.
Modern climate models are more accurate than the instruments in some
cases. The models actually help identify measurement problems in the
real world. And that 'is very' important, because measuring the global climate
is a lot of measuring. The models are so good, they can actually help identify
instrumental aberrations that can then be examined and fixed.
What has been learned?
Using the above processes, mistakes and aberrations from measurements are corrected for with models which are tested against the measurements and then refined.
Absolutely. Continued investigation and testing of the measurements and the models will help refine the models and the measurements as well. Science is about discovery through testing. The scientific method is very careful and methodical. It is the best and only way to understand our climate.
...it may have taken much longer to realize there was a problem in
our atmospheric composition that may be dramatically affecting climate.
The models allowed us to see that the temperature was rising when it
should have been falling.
The models used are called Global Circulation Models (GCM's).
The major forces are fairly well known. So when the global temperature
started doing something other than the model, the lead hypothesis was either something is wrong with the model, or something changed in the
climate system.
Upon further examination...
...it was found that indeed, human GHG output
and aerosols were changing the way our climate system operated. Some
effects had a cooling impact, and some had a warming impact. Both
combined however still lead to further warming.
"Let’s review the successful predictions of the models."
That the globe would warm, and about how fast, and about how much.
That the troposphere would warm and the stratosphere would cool.
That nighttime temperatures would increase more than daytime temperatures.
That winter temperatures would increase more than summer temperatures.
Polar amplification (greater temperature increase as you move toward the poles).
That the Arctic would warm faster than the Antarctic.
The magnitude (0.3 K) and duration (two years) of the cooling from the Mt. Pinatubo eruption.
They made a retrodiction for Last Glacial Maximum sea surface temperatures which was inconsistent with the paleo evidence, and better paleo evidence showed the models were right.
They predicted a trend significantly different and differently signed from UAH satellite temperatures, and then a bug was found in the satellite data.
The amount of water vapor feedback due to ENSO.
The response of southern ocean winds to the ozone hole.
The expansion of the Hadley cells.
The poleward movement of storm tracks.
The rising of the tropopause and the effective radiating altitude.
The clear sky super greenhouse effect from increased water vapor in the tropics.
The near constancy of relative humidity on global average.
The expanded range of hurricanes and cyclones--a year before Cyclone Catarina showed up off the coast of Brazil, something which had never happened before.
"Looks like a pretty good track record to
me. Are there problems with the models, and areas where they haven't
gotten it right yet? Sure there are. The double Inter-Tropical
Convergence Zone which shows up in some coupled models, ENSO
variability, insufficiently sensitive sea ice, diurnal cycles of moist
convection, and the exact response of climate to clouds are all areas
of ongoing research. But the models are still the best thing we have
for climate prediction under different scenarios, and there is no
reason at all to think they're getting the overall picture wrong."
