Evaporative Resistance is of Equal Importance as Surface Albedo in High‐Latitude Surface Temperatures Due to Cloud Feedbacks. Issue 4 (18th February 2020) - Kim, Jinhyuk E.
Abstract: Arctic vegetation is known to influence Arctic surface temperatures through albedo. However, it is less clear how plant evaporative resistance and albedo independently influence surface climate at high latitudes. We use surface properties derived from two common Arctic tree types to simulate the climate response to a change in land surface albedo and evaporative resistance in factorial combinations. We find that lower evaporative resistances lead to an increase of low clouds. The reflection of light due to the difference in albedos between vegetation types is similar to the loss of incident sunlight due to increased cloud cover resulting from lower evaporative resistance from vegetation change. Our results demonstrate that realistic changes in evaporative resistance can have an equal impact on surface temperature to changes in albedo and that cloud feedbacks play a first‐order role in determining the surface climate response to changes in Arctic land cover. Plain Language Summary: In the Arctic, darker land surfaces lead to warmer temperatures because they absorb more sunlight. However, there are multiple types of plants that grow in the Arctic, which differ not only in how dark they are but also how easily they release water. We investigate how different Arctic plants absorption of sunlight and ability to release water to the atmosphere can affect temperature over Arctic land using an Earth System Model. We find that dark trees are capable of absorbing a greater fraction of the incoming sunlight than their brighter counterparts, which tends to warm the surface. In comparison, when the land surface has a harder time releasing water into the atmosphere, a smaller fraction of energy at the land surface is used to evaporate water. This warms the air above the surface, which leads to evaporation of cloud droplets and less cloud cover. As a result, more sunlight is able to reach the surface, and land surface temperatures are warmer even when the surface is relatively bright. In combination, we find that the darkness of the surface and the plants' ability to release water have an equal influence on surface temperatures over land in the Arctic. Key Points: Two Arctic plant types with different properties cause substantial changes to land surface temperature through different physical pathways Reducing land surface evaporative resistance increases low clouds and increases shortwave cloud forcing Albedo directly warms the land surface, while changes in evaporation warms mostly by modifying cloud cover