Some supercomputers can do more than 80 million calculations an hour! Courtesy of UCAR Digital Image Library

How do researchers know whether a computer model of Earth’s climate is accurate? To test accuracy of a model, its results are compared to observed measurements. This is often done by comparing climate data that has been directly measured over the past 100 years with a model run over the same timeframe. If the model and the actual measurements are similar, then the mathematical equations used to describe Earth dynamics are assumed to be relatively accurate.

Some uncertainty about future climate predictions based on models is due to uncertainties in the model. There are processes and feedbacks between different parts of the Earth that are not fully understood and are areas of active research. For example, the effects of clouds on climate is known to be a significant, however researchers are actively trying to better understand the effect of clouds to ensure that climate models accurately portray this part of the Earth system. Researchers work to ensure that natural processes are represented in climate models as accurately as possible, so that models can be used to make predictions of future climate that are as accurate as possible.

The majority of the uncertainty in these climate predictions is not related to natural processes. Instead, it is uncertain how much pollution humans will be adding to the atmosphere in the future. Innovations that stop or limit the amount of greenhouses gases that are produced, legislation that changes the amount of pollutants that are released, and how the growing human population lives in the future are all at least somewhat unknown. To address this, climate models are often run through various scenarios, each addressing pollution and development by humans in a different way.

According to the Intergovernmental Panel on Climate Change, the majority of climatologists agree that climate models do not perfectly represent climate processes. There is always some error in models. However, climatologists don't think that better models would not change the conclusion that Earth’s average temperature is warming.

Some supercomputers can do more than 80 million calculations an hour! Courtesy of UCAR Digital Image Library

Global climate models are used to predict what will happen to Earth’s climate in the future. Groups like the Intergovernmental Panel on Climate Change (the IPCC) compare the results from several different climate models as they figure out what is most likely to happen. But how do scientists know whether a model’s predictions are correct? How do they figure out whether the model is doing a good job at predicting the future of climate change?

To figure out whether a climate model is doing a good job, scientists give it a test. The model is run through a time period for which we have actual measurements of Earth’s climate, the past 100 years for example. The results from the model are compared with the actual measurements of real climate. If the model and the actual measurements are similar, then the math equations in the model that are used to describe how Earth works are probably quite accurate. If the model results are very different from our records of what actually happened, then the model needs some work.

Some uncertainty about our future climate is because there are processes and feedbacks between different parts of the Earth that are not fully understood. These are difficult to include in the models until we understand them better. Today, scientists are conducting research to learn more about how some of the less well-known processes and feedbacks work. For example, the effects of clouds on climate is known to be a large, however it is not fully understood and so scientists are researching clouds to ensure that climate models are as accurate as possible. Scientists work to ensure that natural processes are represented in climate models as accurately as possible, so that models can be used to make predictions of future climate that are as accurate as possible.

Most of the uncertainty in these predictions of future climate is not related to natural processes. Instead, it is uncertain how much pollution humans will be adding to the atmosphere in the future. Innovations that stop or limit the amount of greenhouses gases that are produced, laws and rules that change the amount of pollutants that are released, and how the growing human population lives in the future are all somewhat unknown. To deal with this, climate models are often run several times, each time with different amounts of pollution and development by humans.

According to the IPCC, most climate scientists agree that while climate models are not perfect, they are currently pretty good and better models would not change the conclusion that Earth’s average temperature is warming.

Some supercomputers can do more than 80 million calculations an hour! Courtesy of UCAR Digital Image Library

How will Earth’s climate change in the future? Scientists use climate models to figure that out. But how do they know whether the predictions are correct? How do they figure out whether the model is doing a good job at predicting the future of climate change?

To figure out whether a global climate model is doing a good job, scientists give it a test. They ask the model to predict the climate of the past 100 years. We have real measurements of climate for this time period so the answers are known. The results from the model are compared with the actual measurements of real climate. If the model and the real measurements are similar, then the mathematical equations in the model that are used to describe how Earth works are probably quite accurate. If the model results are very different from our records of what actually happened, then the model needs some work.

Some uncertainty about future climate is because there are things we still do not know about how the Earth works. These things are hard to include in the models until we understand them better. Today, scientists are learning more about how the Earth works to make models even better. For example, clouds have a large effect on climate, but we do not fully understand how they affect the climate, so scientists are studying how models can better include clouds.

Most of the uncertainty in these predictions of future climate is not related to natural processes. What we really do not know is how much pollution humans will be adding to the atmosphere in the future. Inventions that stop greenhouses gases from being added to the air, laws and rules that change the amount of air pollution, and how people live in the future are all somewhat unknown. To deal with this, climate models are often run several times, each time with different amounts of pollution and development by humans.