Impacts of Pacific Ocean warming trends (ImPOse)
Lead Research Organisation:
UNIVERSITY OF EXETER
Department Name: Mathematics
Abstract
The tropical Pacific Ocean is at the heart of global climate variability and change. El Niño and La Niña events consist of large-scale sea surface temperature (SST) anomalies in the equatorial Pacific. By driving global-scale changes in the atmospheric circulation, El Niño and La Niña events cause floods, droughts and temperature extremes across the world. On decadal and longer timescales, even small SST changes in the tropical Pacific can be associated with devastating long-term changes in rainfall patterns, such as the US "Dust-Bowl" drought of the 1930s. Tropical Pacific SSTs are also a primary control of global mean temperature variability, and were a major driver of the "slowdown" in global warming in the early years of this century. The response of the tropical Pacific to climate change is therefore of immense interest and importance.
Climate models consistently project that eastern equatorial Pacific SSTs warm more than surrounding regions under climate change, which is similar to the pattern of SST warming during El Niño events, and acts to reinforce SST anomalies during El Niños. Such behaviour leads to projections with a greater frequency of extreme El Niño events, affecting weather extremes globally. This pattern of SST warming also greatly influences the global pattern of mean precipitation changes and strongly modulates global temperature change (climate sensitivity).
However, observations over the last 50-100 years suggest only a small eastern equatorial Pacific warming trend - which is greatly at odds with the strong trends produced by climate model simulations, potentially invalidating many aspects of future climate projections. The conflict between modelled and observed trends holds across multiple SST datasets and several generations of climate models, including our new pilot analysis of state-of-the-art climate models. These results suggest that climate models are fundamentally misrepresenting the tropical Pacific response to climate change: consequences include projecting incorrect changes in global temperature change, global rainfall patterns, global circulation responses, tropical cyclone activity and air-sea CO2 fluxes.
ImPOse will provide the focused, coordinated approach that is necessary (but has to date been missing) to identify the root causes of model errors in tropical Pacific SST trends, by testing multiple hypotheses using state-of-the-art models/observations and targeted idealised experiments, together with an explicit plan of how to correct model projections by feeding results directly into model development and identifying possible emergent constraints. It is crucial that this serious tropical Pacific error and its impacts on global and regional climate projections are assessed, its cause isolated, and a pathway to correcting it identified.
ImPOse consists of three complementary parts:
1) Analysis of long-term tropical Pacific trends in state-of-the-art observational datasets and climate models.
Through careful analysis of these datasets, including testing several existing hypotheses, we will determine why modelled and observed trends disagree.
2) Idealised climate model experiments to determine fundamental causes of tropical Pacific model biases in present-day climate.
Model biases in the tropical Pacific response to climate change are likely to be strongly linked to biases in the simulation of present-day climate. Targeted model experiments will be performed to test hypotheses about the causes of present-day biases, including both structural and parameter-based causes.
3) Climate model experiments to determine the global impacts of tropical Pacific SST trends.
By comparing the effect of imposed observed vs modelled tropical Pacific SST in a set of climate model experiments, we will determine the global impact of tropical Pacific climate change and assess the credibility of CMIP6 climate change projections.
Climate models consistently project that eastern equatorial Pacific SSTs warm more than surrounding regions under climate change, which is similar to the pattern of SST warming during El Niño events, and acts to reinforce SST anomalies during El Niños. Such behaviour leads to projections with a greater frequency of extreme El Niño events, affecting weather extremes globally. This pattern of SST warming also greatly influences the global pattern of mean precipitation changes and strongly modulates global temperature change (climate sensitivity).
However, observations over the last 50-100 years suggest only a small eastern equatorial Pacific warming trend - which is greatly at odds with the strong trends produced by climate model simulations, potentially invalidating many aspects of future climate projections. The conflict between modelled and observed trends holds across multiple SST datasets and several generations of climate models, including our new pilot analysis of state-of-the-art climate models. These results suggest that climate models are fundamentally misrepresenting the tropical Pacific response to climate change: consequences include projecting incorrect changes in global temperature change, global rainfall patterns, global circulation responses, tropical cyclone activity and air-sea CO2 fluxes.
ImPOse will provide the focused, coordinated approach that is necessary (but has to date been missing) to identify the root causes of model errors in tropical Pacific SST trends, by testing multiple hypotheses using state-of-the-art models/observations and targeted idealised experiments, together with an explicit plan of how to correct model projections by feeding results directly into model development and identifying possible emergent constraints. It is crucial that this serious tropical Pacific error and its impacts on global and regional climate projections are assessed, its cause isolated, and a pathway to correcting it identified.
ImPOse consists of three complementary parts:
1) Analysis of long-term tropical Pacific trends in state-of-the-art observational datasets and climate models.
Through careful analysis of these datasets, including testing several existing hypotheses, we will determine why modelled and observed trends disagree.
2) Idealised climate model experiments to determine fundamental causes of tropical Pacific model biases in present-day climate.
Model biases in the tropical Pacific response to climate change are likely to be strongly linked to biases in the simulation of present-day climate. Targeted model experiments will be performed to test hypotheses about the causes of present-day biases, including both structural and parameter-based causes.
3) Climate model experiments to determine the global impacts of tropical Pacific SST trends.
By comparing the effect of imposed observed vs modelled tropical Pacific SST in a set of climate model experiments, we will determine the global impact of tropical Pacific climate change and assess the credibility of CMIP6 climate change projections.
