Geoengineering to Reduce Climate Change May Severely Impact Rainfall Patterns

As our climate changes, geoengineering is becoming an option that seems more and more attractive. But is this process really an option? Scientists have discovered that reducing the amount of sunlight reaching the planet's surface through this technique may not undo climate change after all and may instead have unwanted effects on Earth's rainfall patterns.

Climate change and global warming itself is altering Earth's water cycle. More water evaporates as temperatures increase, which can dry out some regions while causing more rain to fall in 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 is. Yet in order to find specifically how the water cycle reacts, the scientists used a simple energy balance model.

The researchers examined 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. The scientists predicted the response of the water cycle for two cases and found that in the former, evaporation increased by 2 percent per degree of warming. In the later, this number reached 3 percent.

"These different responses to surface heating are easy to explain," said Axel Kleidon, one of the researchers, in a news release. "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." For example, a stronger greenhouse effect puts a thicker "lid" over Earth's surface, but if there's no addition sunlight then extra evaporation takes place solely due to the increase in temperature. Turning up the heat by increasing solar radiation, though, enhances the energy flow through Earth's surface because of the need to balance the greater energy input with stronger cooling fluxes from the surface. As a result, there's more evaporation and a stronger effect on the water cycle.

These findings don't just have implications for climate change, though. They also have implications for geoengineering. Many geoengineering approaches aim to reduce global warming by reducing the amount of sunlight reaching Earth's surface. Yet when the scientists applied their results to this geoengineering scenario, they discovered that this approach is unlikely to restore the planet's original climate.

"It's like putting a lid on the pot and turning down the heat at the same time," said Kleidon in a news release. "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."

The findings reveal that geoengineering is likely not a viable way to reduce global warming-at least not by blocking sunlight. This reveals how important it is to reduce emissions to help curtail climate change. It also shows what may be in store for the future as our environment continues to shift.

The findings are published in the journal Earth System Dynamics Discussions.