Geoscience Reference
In-Depth Information
A global perspective on projected changes
Projected changes in greenhouse gas and aerosol emissions during the 21st
century are expected to cause further changes in global average temperature,
sea-level and regional climate, including extreme events. The timing of a 4°C
global warming depends on the emissions scenarios and the response simulated
by a range of different climate models (see
Chapter 2
, this volume - Karoly et
al., 2013).
The IPCC (2012) report concluded that it is virtually certain that increases in
the frequency and magnitude of warm daily temperature extremes and decreases
in cold extremes will occur at the global scale in the twenty-first century. It is
very likely that the length, frequency and/or intensity of warm spells or heat
waves will increase over most land areas.
Based on medium and high emissions scenarios (A1B and A2), a 1-in-20-year
hottest day is likely to become a 1-in-2 year event by the end of the twenty-
firstcentury in most regions. Under a low emissions scenario (B1), a 1-in-20-year
event would likely become a 1-in-5-year event.
The IPCC (2012) also found that it is likely that the frequency of heavy
precipitation or the proportion of total rainfall from heavy falls will increase in
the twenty-first century over many areas of the globe. Based on a range of IPCC
emissions scenarios (B1, A1B, A2), a 1-in-20-year maximum daily rainfall event
is likely to become a 1-in-5- to 1-in-15-year event by the end of the twenty-first
century in many regions.
There is medium confidence that droughts will intensify in the twenty-first
century in some seasons and areas due to reduced precipitation and/or increased
evapotranspiration (IPCC, 2012).
.
Average tropical cyclone maximum wind speed is likely to increase, although
increases may not occur in all ocean basins. It is likely that the global frequency
of tropical cyclones will either decrease or remain essentially unchanged (IPCC,
2012).
There is low confidence in projections of small spatial-scale phenomena such
as tornadoes and hail because competing physical processes may affect future
trends and because current climate models do not simulate such phenomena
(IPCC, 2012).
It is very likely that mean sea level rise will contribute to upward trends in
extreme coastal high water levels in the future (IPCC, 2012).
There is low confidence in projections of changes in some intrinsic patterns
of natural climate variability, such as the El Niño-Southern Oscillation (IPCC,
2012).
Extreme events will have greater impacts on sectors with close links to
climate, such as water, agriculture and food security, forestry, health and tourism.
To respond to these challenges, the IPCC (2012) noted that measures that
provide benefits under current climate and a range of future climate change
scenarios, called low-regrets measures, are available starting points for addressing
projected trends in exposure, vulnerability and climate extremes. They have the
