Near-term tropical cyclone risk and coupled Earth system model biases

Area of Science:

• Climate Science
• Atmospheric Science
• Oceanography

Background:

• Current climate models forecast a shift towards an El Niño-like state in the equatorial Pacific due to greenhouse gas warming.
• However, observational data over the past 50 years indicate a trend towards a La Niña-like state, contradicting model predictions.
• This discrepancy suggests potential inaccuracies in how models simulate the equatorial Pacific's response to warming.

Purpose of the Study:

• To highlight the discrepancy between climate model projections and observed trends in the equatorial Pacific.
• To investigate the implications of this discrepancy for future climate risk projections, particularly for tropical cyclone activity.
• To emphasize the need for improved climate models that can capture a broader range of future Pacific warming scenarios.

Main Methods:

• Analysis of discrepancies between existing climate model predictions and observational data for the equatorial Pacific sea surface temperature gradient and Walker circulation.
• Comparison of projected climate impacts (e.g., tropical cyclone activity) with potential impacts inferred from historical El Niño and La Niña events.
• Discussion of the relevance of transient climate responses for near-term climate adaptation.

Main Results:

• Climate models incorrectly simulate the equatorial Pacific's response to greenhouse gas warming, predicting an El Niño-like state instead of the observed La Niña-like trend.
• This modeling error likely leads to inaccurate projections of regional tropical cyclone activity, potentially overestimating activity in the North Pacific and underestimating it in the North Atlantic.
• Other climate-related risks, such as severe convective storms and droughts, may also be projected erroneously.

Conclusions:

• The transient response of climate systems to greenhouse gases is critical for near-term adaptation, despite potential equilibrium state accuracy in models.
• Current climate models may provide misleading projections for regional climate risks over the next several decades.
• There is an urgent need to develop climate projections that encompass a wider spectrum of potential future tropical Pacific warming scenarios, including those reflecting recent observed trends.