structural:summarization
Climate change feedbacks are natural processes which impact how much global temperatures will increase for a given amount of greenhouse gas emissions. Positive feedbacks amplify global warming while negative feedbacks diminish it. Feedbacks influence both the amount of greenhouse gases in the atmosphere and the amount of temperature change that happens in response. While emissions are the forcing that causes climate change, feedbacks combine to control climate sensitivity to that forcing. While the overall sum of feedbacks is negative, it is becoming less negative as greenhouse gas emissions continue. This means that warming is slower than it would be in the absence of feedbacks, but that warming will accelerate if emissions continue at current levels. Net feedbacks will stay negative largely because of increased thermal radiation as the planet warms, which is an effect that is several times larger than any other singular feedback. Accordingly, anthropogenic climate change alone cannot cause a runaway greenhouse effect. Feedbacks can be divided into physical feedbacks and partially biological feedbacks. Physical feedbacks include decreased surface reflectivity (from diminished snow and ice cover) and increased water vapor in the atmosphere. Water vapor is not only a powerful greenhouse gas, it also influences feedbacks in the distribution of clouds and temperatures in the atmosphere. Biological feedbacks are mostly associated with changes to the rate at which plant matter accumulates CO2 as part of the carbon cycle. The carbon cycle absorbs more than half of CO2 emissions every year into plants and into the ocean. Over the long term the percentage will be reduced as carbon sinks become saturated and higher temperatures lead to effects like drought and wildfires. Feedback strengths and relationships are estimated through global climate models, with their estimates calibrated against observational data whenever possible. Some feedbacks rapidly impact climate sensitivity, while the feedback response from ice sheets is drawn out over several centuries. Feedbacks can also result in localized differences, such as polar amplification resulting from feedbacks that include reduced snow and ice cover. While basic relationships are well understood, feedback uncertainty exists in certain areas, particularly regarding cloud feedbacks. Carbon cycle uncertainty is driven by the large rates at which CO2 is both absorbed into plants and released when biomass burns or decays. For instance, permafrost thaw produces both CO2 and methane emissions in ways that are difficult to model. Climate change scenarios use models to estimate how Earth will respond to greenhouse gas emissions over time, including how feedbacks will change as the planet warms.