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Participation in an international effort to assess the current state and projected changes of the climate system

Ngar-Cheung Gabriel Lau

Lau has participated in the drafting process of the last three assessment reports (ARs) of Working Group I (WGI) of the Intergovernmental Panel for Climate Change (IPCC). This scientific body is sponsored by the World Meteorological Organization and Environmental Programme of the United Nations. WGI is concerned with the physical science basis of climate change. Lau has served as a contributing author for AR3 (2001) and AR4 (2007). More recently, he was appointed to the role of lead author for AR5 (2013). In this capacity, his 17-member team was charged with the task of assessing the nature of the variability of myriad atmospheric and oceanic phenomena and their relevance for regional climate change. These phenomena include the principal monsoon systems of the globe, tropical circulation features such as convective zones, Madden-Julian Oscillations and Indian Ocean Dipole, El Nino-Southern Oscillation, annular and dipolar modes, and large-scale storm systems in middle latitudes. The confidence level of simulations and projections by participating computer climate models has been evaluated. The implications of the projected changes in the behavior of the above-mentioned phenomena on the climate conditions in different geographical areas are critically examined.

The major findings of this assessment exercise are as follows:

•The areal coverage and intensity of the global monsoon system is likely to increase, while the monsoon circulation weakens.

• Reduced warming and decreased precipitation in the eastern Indian Ocean, and increased warming and precipitation in the west, will influence East Africa and Southeast Asia rainfall pattern.

• El Nino-Southern Oscillation will remain to be a domain mode of climate variability in the future.

• The global frequency of occurrence of tropical cyclones will likely either decrease or remain unchanged, concurrent with an increase in maximum wind speed and precipitation rates.

• The Southern Hemisphere extratropical storm track is likely to exhibit a small poleward shift.

• The North Atlantic Oscillation is likely to become more positive on average. The positive trend of the Southern Annular Mode in austral summer/autumn is likely to weaken considerably.