Probabilistic assessment of the rate of future climate change

The chapters in this thesis examine the overall rate of future climate change as it relates to the concept of rapid climate change under a probabilistic framework for quantifying climate model uncertainty. The first study uses a simple climate model to estimate the likely range of rates of temperature change associated with the implementation and removal of climate engineering. We found that following the removal of climate engineering, high rates of temperature change were sustained for two decades; rates of change of 0.5 (0.3, 0.1) °C per decade were exceeded over a 20-year period with 15% (75%, 100%) likelihood. Our results suggest that climate engineering in the absence of deep emissions cuts could arguably constitute an increased risk of dangerous anthropogenic interference in the climate system. The second study uses an intermediate complexity climate model to assess the likelihood of varying climate system properties through the use of probability density functions of climate sensitivity and ocean diffusivity. We found that the most probable maximum rate of temperature change occurred between 0.3 and 0.5 °C per decade with a most likely value of 0.36°C per decade. Our results also suggest that changes in ocean diffusivity in the model have a significant effect on the rate of transient climate change in the upper end climate sensitivity simulations, but show little influence in the lower end. Many of the high rates of warming obtained in both studies could potentially cause widespread physical and biological damage, exceeding the adaptive capacity of healthy functional ecosystems.