Record high temperatures and more extreme weather
Climate change and its consequences
Wildfires in Sweden, record highs of over 30°C in the northern Arctic Circle, heat and drought in central Europe, Asia and parts of North America. By the end of August, 2018 was one of the four warmest years of all time and by the end of the year is expected to be among the six warmest since records began.
1. Climate change and greenhouse gases
- It is virtually certain that global warming, especially since the middle of the 20th century, has been primarily caused by mankind. Although fluctuations in the sun’s radiation intensity were partly responsible for warming in the first half of the 20th century, they do not explain the intense warming since then. In fact, in the last few years with the steepest increases in temperature, the sun’s radiation intensity has actually declined.
- Greenhouse gases such as carbon dioxide (CO2) absorb the Earth’s long-wave radiation and reflect a large part of this energy back towards the Earth’s surface. As the concentration of greenhouse gases rises, so does the energy content particularly in the lower atmosphere (troposphere), which heats up. As well as the air, the ground and oceans also become warmer. The portion of the long-wave energy that is increasingly reflected towards the Earth’s surface is not emitted towards space. This is – in addition to the changes in the ozone content due to other causes – the second important reason why the entire stratosphere is cooling down long term. Both trends, the warming low down (troposphere) and the cooling high up (stratosphere), have been recorded and measured for decades. They can only be explained by the greenhouse effect.
- Climate change is bringing more energy into the atmosphere. More water condenses from warmer oceans, and a warmer atmosphere can absorb a greater volume of moisture. Among other things, both these factors increase the potential for heavy rainfall. The increased amount of moisture in the atmosphere means more energy, which is released when the moisture condenses into clouds and the water subsequently freezes. This energy influences the water cycle and fuels convective processes. Regionally, for example in Europe and many other parts of the planet, climate change is also leading to more extreme heat events and in future probably to more agricultural droughts.
2. Global warming in figures
- All 17 years since 2001 rank among the 18 warmest since measurements began.
- 2017 was one of the three warmest years on record. But even more important is the fact that it was the hottest year ever recorded without the warming effect of the natural climate oscillation, El Niño.
- And in all of this, scientists see a clear signal of climate change.
- By the end of August, 2018 was the fourth warmest year on record, also without the influence of an El Niño phase. Based on the plausible scenarios, by end of December it is likely to be at least among the six warmest years ever.
3. Climate change and its effects
- Many scientists believe that climate change is influencing weather hazards such as heatwaves, droughts, extreme precipitation and storms in individual regions. But the link is complex. Natural climate oscillations exert a major – and over shorter periods frequently far greater – influence on weather hazards, and the vulnerability of buildings and infrastructure to natural events as well as the development of preventative structures and regulation also have a major effect on the scale of registered losses. When focusing on one single region and one individual weather hazard, the impact of climatic changes on losses since 1980 (adjusted to take account of rising values) can be identified in some cases. On a global scale, however, such impacts would not show up due to the countervailing influences partially cancelling each other out.
- New research methods enable scientists to state whether in a specific region extreme events such as rain above a certain amount or temperatures above a certain threshold have become more – or less – likely compared with a world without climate change. The results of these so-called attribution studies are of enormous help in the early identification of risk drivers and thus also in planning adaptation and loss prevention measures. Such regional studies have thus far been carried out on heat, drought, precipitation and floods, oceanic parameters, cold and storms, although the majority of studies have looked at temperature extremes. For example, they have revealed that the probability of severe flooding events in certain regions of Great Britain has increased significantly compared with a world without climate change. Of 131 extreme events in different parts of the world investigated in peer-reviewed studies by one scientific journal, 68% revealed an influence of climate change on altered exceedance probabilities. Many extreme events are therefore already being influenced by climate change.
4. Examples of natural hazards that indicate an existing, assumed or future influence of climate change
- Severe thunderstorms in North America: Losses from severe thunderstorms with hail, gusts, tornadoes or torrential rain are rising, even after adjusting to take increasing values into account. This trend tallies with changes in meteorological data and in particular the increase in moisture, which studies have identified as the most significant influencing factor in the lower atmosphere. As the increased moisture content is due to the rising air temperatures and the consequently warmer ocean surfaces, this strongly indicates an influence from climate change. And this also correlates with what scientists expect as a consequence of climate change.
- Severe thunderstorms in Europe: As in North America, normalised losses have increased significantly here. Studies show that in parts of Europe, including southwest Germany, severe thunderstorms with hail have already increased; again, the increase in moisture in the lower troposphere is one of the main reasons for this. Such a change is a consequence of rising temperatures. Greater loss susceptibility of buildings fitted with sensitive thermal insulation, solar installations and expensive metal façades is also driving up loss potentials. The costliest single thunderstorm event since 1980 occurred in Germany in July 2013, when powerful hailstorms in particular caused overall losses of €4.1bn in today’s values. About €3.2bn of this was insured.
- Monsoon and heatwaves in South Asia: In South Asia, and particularly in India, heatwaves are now the events that bring about the most drastic humanitarian consequences. Often, thousands of people die in these summer heatwaves, when temperatures can reach well over 40°C. Scientists consider it “probable” that climate change will bring more frequent and more severe heatwaves to South Asia. It has already been established that the very warm periods have become longer there. The IPCC expects climate change to influence monsoon rainfall in the future. For example, in India average rainfall during the monsoon period is likely to increase slightly, as will fluctuations between seasonal precipitation highs and lows, which would pose a huge problem for agriculture. At the same time, extreme rainfall events are expected to increase. In summary: higher seasonal variability and more extremes.
- Flooding – Uncoupling of meteorology and losses: In Europe, the overall trend in losses (after adjustment for increases in values) has fallen – primarily thanks to improved loss prevention. Nevertheless, and this is significant for the future, scientists are convinced that climate change is influencing precipitation patterns in Europe and globally and will produce heavy rainfall and flash floods more frequently – coupled with a tendency for longer dry phases to occur in Europe and elsewhere. In many regions, heavy rainfall has already increased. According to projections by the IPCC, there will also be more extreme river flooding in many regions. Studies on the US Gulf Coast have revealed that the probability of extreme three-day rainfall, as witnessed in Louisiana in August 2016 (overall losses US$ 10bn) or in August 2018 during Hurricane Harvey, has already increased by a factor of at least 1.4 and 1.5 respectively as a result of climate change.
Over the last few years, there have been several examples of severe river flooding in central Europe, for example in 2013. In terms of its meteorological/hydrological characteristics, the flooding was similar to the 2002 floods along the Elbe and its tributaries, but caused a third less damage. This can be explained by the billions invested in flood protection in Germany and neighbouring countries following the Elbe floods of 2002. Money well spent! In North America and China too, there are indications that massive investment in flood protection on rivers has led to a reduction in normalised losses.
- Tropical cyclones in the North Atlantic and other ocean basins: In the tropical North Atlantic, storm activity is heavily influenced by natural climate oscillations, such as the persistent warm and cold phases in the North Atlantic over many decades (Atlantic Multidecadal Oscillation), or by teleconnection effects from the ENSO climate oscillation in the Pacific – better known as El Niño and La Niña. Since the last warm phase began in the mid-1990s, there has been a high variability in the number of major hurricanes per season – but no trend. In some ocean basins, there has for several decades been a poleward shift in the latitude at which tropical cyclones generally reach their maximum intensity. A causal connection to climate change of this observed shift has already been analysed for the western part of the North Pacific; it is projected to continue in the future. Cautious statements are possible regarding the future of tropical cyclones: as a result of climate change, scientists expect no increase in the overall number of storms, but a higher proportion of severe storms. They postulate that, as a result of global warming, higher layers of the troposphere could become drier and wind shear could increase, thus inhibiting the formation of tropical storms. However, at the same time, the energy potential increases with the higher water temperatures. In future, therefore, a higher proportion of storms may become extremely powerful.
Greater protection against and adaptation to the consequences of natural disasters is urgently needed to prevent the unchecked growth of their humanitarian and financial impact. Insurance cover can go some way to cushioning the financial losses and strengthening resilience against economic shocks, which would clearly benefit the individuals and economies affected.