A key question in climate science is how the global mean surface temperature responds to changes in greenhouse gases. This dependency is quantified by the climate sensitivity, which is determined by the complex feedbacks in the climate system. In this study observations of past climate change are used to estimate this sensitivity. Our estimate is consistent with values for the equilibrium climate sensitivity estimated by complex climate models but sensitive to the use of uncertain input data.

Moisture recycling is the atmospheric branch of the water cycle, including evaporation and precipitation. While the physical water cycle is well-understood, the social links among the recipients of precipitation back to the sources of evaporation are not. In this work, we develop a method to determine how these social connections unfold, using a mix of quantitative and qualitative methods, finding that there are distinct types of social connections with corresponding policy and management tools.

Human-caused, climate change hazards in the ocean continue to aggravate over a very long time. For business as usual, we project the ocean oxygen content to decrease by 40% over the next thousand years. This would likely have severe consequences for marine life. Global warming and oxygen loss are linked, and meeting the warming target of the Paris Climate Agreement effectively limits related marine hazards. Developments over many thousands of years should be considered to assess marine risks.

Using climate simulations, we investigate the role of water recycling in shaping the climate of low-obliquity Earth-like terra-planets. By such a mechanism feeding water back from the extra-tropics to the tropics, the planet can assume two drastically different climate states differing by more than 35 K in global temperature. We describe the bifurcation between the two states occurring upon changes in surface albedo and argue that the bistability hints at a wider habitable zone for such planets.

Large volcanic eruptions are a large source of uncertainty for decadal climate predictions. Two decadal forecasts with different initial conditions are performed to assess the question of how pre-eruption climate states influence the impact of the volcanic signal on the predictions. We show that the average global cooling response and precipitation decrease is relatively robust, but on a regional and seasonal scale, we find substantial differences that are dependent on the initial conditions.