Climate change & climate protection

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How will climate change alter the landscape of natural hazards and risks over the long term?

In order to develop scientific scenarios showing the long-term impacts from climate change, the potential paths for the development of greenhouse gas concentrations in the atmosphere need to be fed into the climate models. In this context, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) – published in 2013 and 2014 – defines the Representative Concentration Pathways (RCP), which also indicate the extent to which radiated energy per area and time (radiative forcing) will have increased due to anthropogenic factors by the end of the 21st century compared to the pre-industrial period. For example, RCP2.6 is a scenario in which the maximum level of radiative forcing from greenhouse gases resulting from human activity will have been reached by 2050, and with a level of approximately 2.6 W/m2 of radiative forcing caused by human activity by the end of the 21st century relative to the pre-industrial level. In this scenario, mankind would still be able to approximately keep within the 2-degree target by the end of the 21st century, with an increase in temperature of 1.6 [0.9 – 2.3]°C. On the other hand, the RCP8.5 scenario envisages a strong increase in radiative forcing of 8.5 W/m2, resulting in a global mean temperature increase until the end of the century of 4.3 [3.2 – 5.4]°C relative to pre-industrial times – more or less the pathway mankind is on track as per 2014.

One of the key statements in the Fifth Assessment Report of the IPCC is the expectation that what is known as hydroclimatic intensity will be exacerbated by continuing climate change. This means that regions that are already humid today, for example the humid tropics, will become even more humid, and areas that are dry today, such as subtropical regions, will become even drier (and in some cases warmer too).  The latter development towards more dryness will most probably affect Mediterranean countries, the Southwest and Southeast of the USA, Mexico, Central America and parts of South America, Southern Africa and parts of Australia. This trend will have a significant impact on agriculture and forestry in the form of increasing yield variability and a growing pressure to adapt. In regions that become more and more arid, there will be an increasing need to water agricultural crops, and the range of species of crop plants will need to be adapted to the changing conditions. Individual extreme events, such as long heatwaves and periods of drought, could occur in these areas more frequently in the future.

Heat and drought

According to the projections, heat and drought will also increase in many regions of the temperate zone, in Europe for example. This means that yield variability and the pressure to adapt will also increase for agriculture and forestry here. Scenarios will also be more probable in which extreme heat/drought leads to restrictions in the amount of cooling water available to generate electricity from thermal power plants, and eventually to shutting down these plants. In weather conditions like these, there will also be less electricity available from wind power, while electricity demand for air conditioning is at its maximum.

Intense rainfall

The projections envisage an increase in intense rainfall in many land areas in the temperate zones and the humid tropics. In the RCP8.5 scenario in particular, the changes that occur will be strong. This will increase the flash flood hazard. Likewise, river floods are projected to become more frequent in many parts of the world. Under RCP2.6, the number of people exposed to a one-in-100-year flooding event (as measured in the 20th century) will increase roughly fourfold by the end of the 21st century, under RCP8.5 it will increase fourteen fold.

Severe thunderstorms

Surface humidity, which is an essential requirement for the formation of intense rainfall and severe thunderstorms, will increase in tandem with the evaporation rate of the oceans (in other words their surface temperature), and with air temperature, which determines the capacity for humidity. The Fifth Assessment Report of the IPCC specifically states that scientific findings are suggestive of a trend towards environments favouring more severe thunderstorms as a result of climate change, but the small number of studies precludes any probability assessment of this change. A study conducted by Munich Re in collaboration with the German Aerospace Centre (DLR) was able to demonstrate an increase in severe thunderstorm situations and assigned normalised losses over the last forty years for the USA; other studies have already shown indications for increasing formation of intensive severe thunderstorms including hail in the European region for northern Italy, France and southwest Germany over the past decades.

Winter storms

The rainfall associated with European winter storms will most probably increase because there is more water vapour in the air. The northerly shift in storm tracks will continue, but this will not be the only effect of climate change. Several model studies show an increase in the extreme wind speeds from such storms in parts of Europe. However, in general, because of persisting model uncertainties, there is still low confidence in projections of regional changes in storm tracks.

Tropical cyclones

As regards tropical cyclones, increases in maximum wind speeds and precipitation rate are expected due to climate change, but their global frequency will likely either remain unchanged or decline.  Even though there is only low confidence in regional projections for changes in intensity and frequency, it is according to the IPCC more likely than not that the frequency of very intensive tropical cyclones will substantially increase in some basins (particularly in the North Atlantic  and the Western North Pacific). It is highly probable that the storm surge and wind hazards will increase at the exposed coastlines along with this change.

Sea level rise

The projected rise in sea level varies considerably along the different coastlines. Under the RCP8.5 scenario, the global mean sea level in the period 2081-2100 will be around 0.45-0.82 m higher relative to the period 1986-2005. The increase will be greater along some coastlines, e.g. in north-east America and in parts of Asia. This will increase the exposure of coastal cities, infrastructures such as harbours, etc.

Permafrost

Thawing of the surface permafrost in the northern latitudes of Asia and North America, as well as in the high mountain regions, brings with it an increasing exposure for infrastructure such as pipelines, railways and overhead transmission lines, for settlements as well as for facilities for the exploration and exploitation of natural resources such as natural gas.

The increasing navigability of the Northeast and Northwest Passages (under the RCP8.5 scenario, large portions of the Arctic Ocean will already be mostly ice-free in late summer by the mid-21st-century) will introduce new exposure and hazards in these regions - for shipping and coastal areas (port facilities, industrial plants).

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