Studying how and why climate change varies with latitude from the equator to the poles
When discussing climate change, it is common to talk in terms of global trends, e.g., periods of “global warming” or “global cooling”. But, often these globally-averaged trends have different values at different latitudes.
An important factor to consider is how climate change varies with latitude from the equator to the poles.
In particular, during periods of global warming or cooling, the temperature changes tend to be smallest at the equator and largest at the poles. This phenomenon is sometimes called “polar amplification”. Because the poles are much colder than the equator, this means that in times of global warming, the temperature difference between the poles and the equator get slightly smaller, while during times of global cooling, the differences get slightly larger.
In Soon and Legates, 2013, we studied the changes in this “Equator-to-Pole Temperature Gradient” (or EPTG for short) for the Northern Hemisphere. We found that the changes were very closely related to changes in the Sun’s output, which we estimated using the Hoyt and Schatten (1993) dataset. This suggests that the changes are mainly driven by solar variability.
For more details, see:
Soon and Legates, 2013. Solar irradiance modulation of Equator-to-Pole (Arctic) temperature gradients: Empirical evidence for climate variation on multi-decadal timescales. Journal of Atmospheric and Solar-Terrestrial Physics. Vol. 93, pp45-56. https://doi.org/10.1016/j.jastp.2012.11.015; (🗄️)
More recently, we looked at how the East Asian and Australian summer monsoons changed over the last 1000 years using paleo-hydrology records derived from lake sediment cores, corals, stalagmites, etc. It has long been thought that the areas affected by these monsoon seasons both moved south during the Little Ice Age. This was a relatively cold period between about 1400 AD and 1850 AD.
However, we found that this is not quite true. While we found that the East Asian Summer Monsoon did indeed move south during this cold period, the Australian Summer Monsoon moved north. That is, during cold periods, the monsoon regions seem to move towards the equator and shrink in size. During warm periods, the regions expand and move away from the equator.
For more details, see: Yan, Wei, Soon et al. (2015). Dynamics of the inter-tropical convergence zone over the western Pacific during the Little Ice Age. Nature Geoscience, Vol. 8, p315-320. https://doi.org/10.1038/ngeo2375; (🗄️)