Accounting for Pacific climate variability increases projected global warming

Area of Science:

• Climate science
• Climate modeling
• Global warming

Background:

• Observational constraints aim to reduce uncertainties in climate model projections.
• Internal climate variability, particularly the "pattern effect" in the eastern tropical Pacific, has historically weakened the observed global warming trend.
• This variability has led to underestimations of recent warming trends.

Purpose of the Study:

• To refine projections of future global warming by addressing the influence of internal climate variability.
• To re-evaluate the likelihood of exceeding critical warming thresholds, such as 2°C, under different emissions scenarios.
• To improve the accuracy of climate change predictions for better adaptation planning.

Main Methods:

• Utilized observational constraint methods linking past global warming trends to climate model projections.
• Developed a novel approach by regressing out internal climate variability from the eastern tropical Pacific before applying observational constraints.
• Applied the observed global mean warming trend as a constraint to refine future warming ranges.

Main Results:

• The refined method produced higher and narrower twenty-first-century warming ranges compared to previous approaches.
• Under a low-emissions scenario, global warming is now projected to likely exceed 2°C, contrary to previous assessments by the Intergovernmental Panel on Climate Change.
• Limiting global warming to well below 2°C presents a greater challenge than anticipated.

Conclusions:

• Internal climate variability significantly impacts the reliability of observational constraints on climate models.
• Future global warming may be more severe than previously estimated, necessitating more ambitious mitigation efforts.
• Reduced uncertainty in refined projections can aid in more effective climate change adaptation strategies.