IPCC AR5 WGI Chapter 14 - A Review
Climate Phenomena and their Relevance for Future Regional Climate Change
Frequently Asked Questions
How is Climate Change Affecting Monsoons? (FAQ 14.1)
Monsoons dominate seasonal climate variation in the tropics, and contribute a large percentage of the annual rainfall in many areas, such as India. Monsoon dynamics are linked to climate change in several ways (FAQ 14.1, Fig. 1). The monsoon circulation is driven by differences in land and sea temperatures, which are changing as the climate warms. Because the land surface warms more rapidly than the ocean surface due to the thermal inertia of the latter, this temperature contrast is increasing in most areas. However, monsoon circulation is actually weakening as the climate warms due to energy balance considerations in the tropical atmosphere.
The duration and amount of monsoon rainfall is contingent upon the moisture content of the air, which is also temperature dependent. As the atmosphere warms, the air can hold more moisture, therefore leading to an increase in the total monsoon rainfall despite the predicted weakening of monsoon circulation. This is the strongest effect of climate change on monsoons; climate models for the 21st century project a 5-15 % increase in global monsoon rainfall as well as an increase in the total surface area seasonally affected by monsoons as tropical regions expand poleward in a warming climate.
How are Future Projections in Regional Climate Related to Projections of Global Means? (FAQ 14.2)
Regional climate change and global mean change are complexly related. Different regional climates respond differently to changes in global climate depending on their location and the importance of smaller-scale climate phenomena such as El Niño. External forcings (e.g., solar radiation) and surface conditions (e.g., topography) vary spatially and therefore affect different regions differently in terms of climate. Additionally, weather systems and ocean currents efficiently redistribute heat and moisture across the globe, further distorting the global mean change on a regional scale. Projected 21st century changes in both surface temperature and precipitation exhibit significant regional variations (FAQ 14.2, Fig. 1). For example, amplified surface warming in the Arctic is projected due to large albedo feedbacks operating at high latitudes as snow and ice melt. Future precipitation changes are even more spatially heterogeneous than temperature changes due to the effects of regional climate phenomena such as monsoons.
FAQ 14.1, Figure 1 | Schematic diagram illustrating the main ways that human activity influences monsoon rainfall. As the climate warms, increasing water vapour transport from the ocean into land increases because warmer air contains more water vapour. This also increases the potential for heavy rainfalls. Warming-related changes in large-scale circulation influence the strength and extent of the overall monsoon circulation. Land use change and atmospheric aerosol loading can also affect the amount of solar radiation that is absorbed in the atmosphere and land, potentially moderating the land–sea temperature difference.
FAQ 14.2, Figure 1 | Projected 21st century changes in annual mean and annual extremes (over land) of surface air temperature and precipitation: (a) mean surface temperature per °C of global mean change, (b) 90th percentile of daily maximum temperature per °C of global average maximum temperature, (c) mean precipitation (in % per °C of global mean temperature change), and (d) fraction of days with precipitation exceeding the 95th percentile. Sources: Panels (a) and (c) projected changes in means between 1986–2005 and 2081–2100 from CMIP5 simulations under RCP4.5 scenario (see Chapter 12, Figure 12.41); Panels (b) and (d) projected changes in extremes over land between 1980–1999 and 2081–2100 (adapted from Figures 7 and 12 of Orlowsky and Seneviratne, 2012).