If you think it’s been getting hot in here, you’re not alone. Computer models of the Earth’s climate tell us that the planet will be heating up in the future. The only question is, how much?
Predictive computer models, extensively used for applications ranging from outguessing the stock markets to forecasting population sizes, have yet to reach a consensus on what the Earth’s climate will be like in 100 years.But they agree it will be much warmer. Climate scientists today study models that predict future climates and pinpoint the significant disparities between them.
At a recent lecture at U of T, Dr. Alex Hall of UCLA’s Department of Atmospheric and Oceanic Sciences discussed the wide range of temperature increases predicted by different climate models.
“By the year 2100, the warming is anywhere from between 1½ and 5½ [degrees Celsius]. So this is a really big difference from simulation to simulation. And part of the uncertainty stems…from differences in the way important feedback processes are represented in the climate [simulations].”
Hall explained that the variance in climate predictions is partly due to different assumptions each one makes about the processes of climate change.
One of the crucial processes is the reflection of sunlight off the surface of the earth back into the atmosphere and outer space. Snow, a surface that reflects up to 90 per cent of solar radiation, is a major contributor to the Earth’s reflectivity, known as its albedo. As rising temperatures melt snow, the planet’s overall albedo decreases-which could lead to a positive feedback loop where more snow melts as temperatures rise. However, different climate models report a wide large range of strength to snow’s albedo effect when predicting global warming.
For all the disagreement over the albedo effect, it is only one of a vast number of factors that must be considered when making climate predictions. Programs that calculate changes in the global climate are among the most complicated computer models in use today. Professor Richard Peltier, director of the recently formed Centre for Global Change Science at U of T, explained how current models work.
“There are four main components [of climate]: atmosphere, ocean, sea ice and land surface processes…We [factor in the sun’s effect on the earth] and explicitly compute the way they interact with each other.”
Current prediction models need supercomputers to handle the myriad factors: ocean currents, carbon dioxide emissions, incoming sunlight, air flow, ice sheet growth or shrinkage, and cloud formation are but a few of the factors in the incredibly complicated calculations.
Peltier explained that the models are hundreds of thousands of lines of code.
“These models are a huge accomplishment of the modern scientific community, representing 50 years of work,” he said.
With the help of atmospheric and surface temperature measurements gathered by weather balloons over the years, it is possible to compare the accuracy of various models.
“The best measure is not that the models fit the data. It’s that predictions we made 15 years ago are right today,” said Peltier.
Although global warming remains a contentious topic in the media, the scientific community has reached a consensus, bolstered by the track record of modern computer modelling. The mathematics and methods of computer climate modelling are complex, but the different models used all agree on one thing: climate change is happening now.
“In the informed scientific community,” said Peltier, “there are effectively no dissenters.”
