In the era of global empires powered by sail, trade winds were once the foundation of vast economies. While the days of tall ships may have passed, new research has revealed that these trade winds may again affect the world’s economies, this time through their impact on global warming.
Recent research published in Nature Communications indicates changes to the Pacific Ocean and its effect on trade winds could see us in for a period of accelerated warming of global surface temperatures.
It’s all because of an ocean-atmosphere interaction known as the Pacific Walker Circulation.
Climate models have long projected that the Pacific Walker Circulation, which includes trade winds that blow from the east to the west across the tropical Pacific Ocean, will decline in strength as the globe warms.
However, that theory took a bit of a hit in the period 1992-2011 when even as more heat continued to accumulate in the Earth system, there was an unprecedented increase in these trade winds. This increase also corresponded with a temporary hiatus in the rise of global surface temperatures even as the deeper oceans continued to warm.
A number of questions arose from this relationship.
- Was the increase in Pacific trade winds and the consequent slowing in global surface temperature rise connected?
- Was this “unprecedented” increase in the Pacific trade winds within the bounds of natural variability and what was the range of natural variability anyway for the Pacific Walker Circulation?
- Finally, if there was a connection between the natural variability of the Pacific Walker Circulation and the slowdown in global surface warming, does this impact the reliability for projections of future surface air temperatures?
To find answers to these questions, CLEX researchers and colleagues examined the response of three fully coupled global climate models. Each of the climate models ran from different initial states and were subjected to increasing greenhouse forcing.
Through this process the researchers aimed to quantify the uncertainties in the estimates of future surface warming due to natural variations in the Pacific Walker Circulation and distinguish any associated regional signatures.
They found that the Pacific Walker Circulation showed large natural changes over decadal timescales associated with a low-frequency climate phenomenon called the Interdecadal Pacific Oscillation or IPO.
The negative phase of the IPO corresponds with stronger trade winds and slower global surface warming. Positive IPO corresponds with weaker trade winds and accelerated global surface warming. This means that the slow march of global warming becomes stronger or weaker for decadal periods depending on the phase of the IPO and the strength of the Trade winds.
Moreover, the future evolution of the IPO was found to be partially predictable, meaning that we can estimate if trends over coming decades will be faster or slower than average. With indications that the negative Interdecadal Pacific Oscillation is now becoming positive, this suggests that the hiatus period is over and we are likely entering a phase of accelerated warming of global surface air temperatures.
- Paper: Bordbar, M. H., England, M., Sen Gupta A., Santoso, A., Taschetto, A. S., Martin, T., Park, W., & Latif, M. Uncertainty in near-term global surface warming linked to tropical Pacific climate variability. Nature Communications. 10, Article number: 1990 (2019). Doi: 10.1038/s41467-019-09761-2