December 5, 2013
Reversing Climate Change Cannot Be Accomplished Via Geoengineering: Researchers
Lee Rannals for redOrbit.com - Your Universe Online
The team used a simple energy balance analysis to explain how the Earth’s water cycle responds differently to heating by sunlight than it does to warming due to a stronger atmospheric greenhouse effect. They show that this difference implies that reflecting sunlight to reduce temperatures may have unwanted effects on the Earth’s rainfall patterns.
Global warming causes more water to evaporate in the air as temperatures increase, effectively drying out some regions, while at the same time adding more rainfall to others due to the excess moisture in the atmosphere. The more water evaporates per degree of warming, the stronger the influence of increasing temperature on the water cycle. However, the latest study shows the water cycle does not react the same way to different types of warming.
The team used the energy balance model to determine how sensitive the water cycle is to an increase in surface temperature due to a stronger greenhouse effect and to an increase in solar radiation.
“These different responses to surface heating are easy to explain,” stated Axel Kleidon of the Max Planck Institute for Biogeochemistry in Jena. “The temperature in the pot is increased by putting on a lid or by turning up the heat – but these two cases differ by how much energy flows through the pot,”
Stronger greenhouse effects lead to a thicker “lid” over the Earth’s surface, but if there is no additional sunlight then extra evaporation takes place due to the increase in temperature. Turning up the heat by increasing solar radiation can enhance the energy flow through the Earth’s surface due to the need to balance the greater energy input with stronger cooling fluxes from the surface.
Many geoengineering approaches try to reduce global warming by reducing the amount of sunlight reaching the Earth’s surface. However, when the team applied their results to a geoengineering scenario like this, they found out that simultaneous changes in the water cycle and the atmosphere cannot be compensated for at the same time. This scenario would mean that reflecting sunlight by geoengineering is unlikely to restore the planet’s recent climate.
“It’s like putting a lid on the pot and turning down the heat at the same time,” Kleidon said in a statement. “While in the kitchen you can reduce your energy bill by doing so, in the Earth system this slows down the water cycle with wide-ranging potential consequences,” he says.