Energy balance points to man-made climate change - physicsworld.com
Reto Knutti and Markus Huber at the Institute for Atmospheric and Climate Science in Zurich, Switzerland, have developed a model based on the simple fact that Earth's energy must be conserved. When the Earth is in equilibrium, the thermal energy it emits is equal to the amount of energy received from the Sun. However, evidence shows that this energy balance has become disrupted, with less energy being emitted back into space. The trapped energy in the climate system thus acts to heat up our planet, causing a rise in global temperature.
The researchers used their energy-balance model to investigate the cause and magnitude of this warming. The model, driven by observational records of climate forcings, surface temperature and ocean heat uptake, was run many thousands of times with different parameter combinations. The combinations that best matched the observations were then fed through the model a second time in order to simulate the climate response to each individual forcing.
The model predicts a global temperature increase of 0.51 °C since the 1950s, similar to the observed estimate of 0.55 °C. Greenhouse gases provide the largest contribution to this warming, responsible for a temperature increase of 0.85 °C, with approximately half of this greenhouse warming offset by the negative forcing of aerosols. On the other hand, the contribution of solar and volcanic forcing was close to zero.
The model was also used to simulate the future evolution of the climate system. A temperature increase of 1.29 °C was found for 2050–2059 compared with the 2000s, almost entirely due to greenhouse gases, with carbon dioxide being the dominant contributor.
These findings are consistent with the latest report by the Intergovernmental Panel on Climate Change (IPCC), as well as other studies that use the optimal fingerprinting approach. The researchers believe that their energy-balance model can be used in tandem with alternative climate-attribution methods.
"We don't criticize optimal fingerprinting – it is a very powerful technique – but to almost all people it's a black box," says Reto Knutti. "It's statistically complex, makes a number of assumptions and is not physically intuitive. At least to a physicist, conservation of energy is fundamental. The fact that our results are entirely consistent with optimal fingerprinting is an argument for even higher confidence in human-induced climate change."
The researchers used their energy-balance model to investigate the cause and magnitude of this warming. The model, driven by observational records of climate forcings, surface temperature and ocean heat uptake, was run many thousands of times with different parameter combinations. The combinations that best matched the observations were then fed through the model a second time in order to simulate the climate response to each individual forcing.
The model predicts a global temperature increase of 0.51 °C since the 1950s, similar to the observed estimate of 0.55 °C. Greenhouse gases provide the largest contribution to this warming, responsible for a temperature increase of 0.85 °C, with approximately half of this greenhouse warming offset by the negative forcing of aerosols. On the other hand, the contribution of solar and volcanic forcing was close to zero.
The model was also used to simulate the future evolution of the climate system. A temperature increase of 1.29 °C was found for 2050–2059 compared with the 2000s, almost entirely due to greenhouse gases, with carbon dioxide being the dominant contributor.
These findings are consistent with the latest report by the Intergovernmental Panel on Climate Change (IPCC), as well as other studies that use the optimal fingerprinting approach. The researchers believe that their energy-balance model can be used in tandem with alternative climate-attribution methods.
"We don't criticize optimal fingerprinting – it is a very powerful technique – but to almost all people it's a black box," says Reto Knutti. "It's statistically complex, makes a number of assumptions and is not physically intuitive. At least to a physicist, conservation of energy is fundamental. The fact that our results are entirely consistent with optimal fingerprinting is an argument for even higher confidence in human-induced climate change."
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