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Detailed presentation of key topics of focus related to climate services

Climate change - an overview

Earth's changing climate will have a lasting impact on all our society's economic, social and political activities. But what exactly is meant by "climate change"? What do we know, and what can we do?

These are the issues addressed in the following:

The climate - a delicate balance

The parameters used to describe the weather – such as temperature, precipitation, wind, humidity and radiation – are in general also the same as those used to define the climate. Climate itself is the totality of weather phenomena which characterise the state of the atmosphere at a particular location or over a more or less large area. It is represented by general statistical properties (such as averages, extreme values, frequencies, lengths of duration etc.) over a sufficiently long period of time. In general, statistics refer to a period of 30 years, known as the standard reference period, although other shorter periods of time are also often used.

However, there is more to the climate than just the atmosphere: it is the outcome of the complex interplay of all the various elements which make up the Earth's ocean-atmosphere system. These include the cryosphere (ice), the biosphere with its seasonal changes in vegetation, the land surface and the Earth's crust. Our climate is determined by a natural balance of incoming short-wave solar radiation to the Earth and outgoing long-wave terrestrial radiation from the Earth's lower atmosphere. Unless the radiative forcing, of approximately 340 W/m2, delivered by the sun at the top of the atmosphere is counterbalanced by an adequate loss of long-wave radiation energy, the Earth-atmosphere system will warm up or cool down.

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Human life depends on the greenhouse effect

"Greenhouse gases", such as water vapour (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) – to name only the most important of these gases – absorb more long-wave radiation than short-wave solar radiation. This leads to warming of the lower atmosphere. Without the trace gases which are naturally present in the atmosphere and without the greenhouse effect the mean temperature of the Earth would be around 32°C lower than it is at the present time. This would make the planet uninhabitable, at least for humans.

Greenhuose effect

Human activities are known to bring about an increase in greenhouse gas concentrations. Around 34 billion tonnes of CO2 are currently emitted to the atmosphere every year. 75% of these emissions come from the use of fossil fuels. The remainder is mainly due to deforestation. Because CO2 and other greenhouse gases (such as methane, nitrous oxide) remain in the atmosphere for such a long time, higher concentrations of CO2 and other greenhouse gases accumulate in the atmosphere over the course of decades.

Atmospheric concentrations of important  global warming gases over the last 10,000 yearsAtmospheric concentrations of important global warming gases over the last 10,000 years Source: IPCC 2007 (WGI-AR4, Summary for Policymakers, Feb. 2007)

This process of concentration adversely affects the spectrum of outgoing long-wave radiation emitted from the Earth-atmosphere system. The temperature increases which then take place in the lower atmosphere are known as the anthropogenic greenhouse effect.

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Where are we taking the climate train?

Discussion of the human drivers of climate change – as opposed to natural factors, such as variations in the Earth's orbit around the sun and in solar radiation, as well as interacting forces within the climate system itself – first began in the 1970s. Meteorologists and atmospheric chemists were already aware of the influence which some trace gases have on the atmosphere's radiation balance. Measurements already showed parallels between rising temperatures and increasing concentrations of CO2. In recent years and decades, it has become increasingly apparent from the evaluation of measurements that previously recognised mean values, frequency distributions and other statistical properties have been changing at an unprecedented rate (see Climate monitoring).

Zeitreihen der CO2-Konzentration und der LufttemperaturZeitreihen der CO2-Konzentration und der Lufttemperatur

Climate scientists' initially uncertain conclusions were based on the simple assumptions originally made about the atmosphere by some models. Over the course of time, however, models have become increasingly complex. Apart from the atmosphere, newer models take account of other components of the climate system, such as the ocean. Today, forecasts of future socio-economic developments in the decades ahead make up an important element of climate forecast models. These have been validated on the basis of climate data from the past. This means that, rather than forecasting the unknown future, these new models work from measurements taken over a documented period of time. The accuracy of models can be estimated by comparing the results they produce with actual observed measurements of climate change.

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Global temperatures will rise between two and five degrees by 2100

In 1988, the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) founded the Intergovernmental Panel on Climate Change IPCC. The main task of this intergovernmental panel is to collate information on climate change, assess the risks of a changing climate and elaborate options for adaptation and mitigation. The IPCC reports on its findings every few years. The most recent Fourth IPCC Assessment Report was released in 2007 in four sub-reports. The report is the outcome of six years of work by 450 lead authors, 800 contributing authors and a further 2,500 experts from more than 130 countries. Scientists as well as numerous government representatives also took part in the complex review processes which led to the drawing up of the Assessment Report. The IPCC was jointly awarded the Nobel Peace Prize together with Al Gore in 2007. The next Fifth Assessment Report is due for release in late 2013.

The IPCC's findings are unequivocal: the world will become significantly warmer. The fact that the forecasts of the rise in global mean temperature (between +2°C and +5°C) vary so much reflects the difficulties researchers have in determining the precise scale of future emissions of greenhouse gases, in particular. Various socio-economic and technological trends (SRES scenarios), each with different impacts on the climate, were considered.

In its next Assessment Report, the IPCC will adopt Representative Concentration Pathways (RCPs) instead of SRES scenarios. RCPs differ from SRES both in the way they are produced and in the characteristic parameters they take into account. In particular, RCPs account better for the impact of potential emission reduction and adaptation strategies. More detailed information about the new RCPs is available here.

Multi-model averages and assessed ranges for surface warmingMulti-model averages and assessed ranges for surface warming Source: IPCC 2007 (WGI-AR4, Summary for Policymakers, Feb. 2007)

However, returning to the latest IPCC Assessment Report: if current trends continue in the worst case development scenario ("business as usual" in the industrialised countries and significantly rising emissions in developing countries) we must anticipate an increase in temperature of +5°C. In the best case, i.e. short-term reductions of over 50% in emissions of CO2, temperatures would still rise by at least +2°C, which is twice the rate of temperature increase in the past 100 years. This increase would be greater than any natural climate variability over the last 10,000 years. Nonetheless, the IPCC established without dissent that the climate could just about "cope" with a global rise in temperature of +2°C. This means that ecosystems, food production and economic development can for the most part adapt to change on this scale. This would, however, imply reducing CO2 emissions globally by 50% and in the industrialised countries by as much as 80%.

Patterns of climate change are uneven in different parts of the world. The continents at mid and northern latitudes and the Antarctic will warm up more, the oceans less. Some regions may even become cooler, while temperatures in other parts of the world will rise by significantly more than the quoted +2°C to +5°C.

Änderung der mittleren Lufttemperatur für verschiedene Emissionsszenarien und ZeiträumeSource: Quelle: IPCC 2007 (WGI-AR4, Summary for Policymakers, Feb. 2007)


Source: IPCC 2007 (WGI-AR4,  Summary for Policymakers, Feb. 2007)

Not only are temperatures rising, the entire climate, including precipitation for example, is changing. The tropics and northern latitudes can expect more precipitation while north Africa, the Mediterranean region and southern Europe will become a great deal drier – particularly during the summer.

The mean changes in climate parameters are also linked to shifts in statistical distributions, such as in extreme values. Even small changes in mean values can have quite considerable impact on the statistical distribution of extreme values.

This will affect people, economies and ecosystems. Higher maximum temperatures will lead to higher rates of mortality among older people. More hot days and heat waves pose the threat of lost harvests. More and more intensive precipitation will result in more erosion and damages and rising insurance costs. We will need less energy for heating, but more energy for air conditioning. Sea level rise will have an impact on coastal countries, island nations and river delta areas. And there are many other examples as well.

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Climate change will also change our life in Germany

If it was possible to slow down the increase in global greenhouse gas concentrations in the future as set out in the SRES scenario A1B, the IPCC projections suggest that the following changes would take place in Germany by 2050

  • Summer temperatures will be between 1.5°C and 2.5°C higher than in 1990
  • Winters will be between 1.5°C and 3°C warmer
  • Summer precipitation may be up to 15% lower
  • Winters may have up to 10% more precipitation.

The statement on the problems associated with climate change issued by the German Meteorological Society on 9 October 2007 briefly summarizes the changes which can be anticipated in Germany in the next 3 decades:

Weather elementAnticipated changeReliabilityImpact
Temperature1,7 °C warmer than in 1900, particularly winters and nightsVery good

Earlier emergence of plants

Increased heat stress

Thawing of permafrost in the Alps (more rockfalls)

Periods of extreme heatMore frequent, more severe Very good

High impact on health

Stress for the biosphere

More forest fires

Alpine glaciersReduction in area of 60% and of mass of 80% since 1850 Very goodExtreme fluctuations in run off
Seal-level rise Approximately 10 cm higher than today Very goodThreat to the North Sea and Baltic Sea coasts
Precipitation

Drier summers, wetter autumns and winters with more rain and less snow,

Unprecedentedly high amounts of precipitation on single occasions

Good Greater danger of flooding (in part due to undersized drainage systems)
Dry or drought periods More frequent Reasonable

Agriculture, the energy sector and inland waterway transport affected

Greater risk of forest fires

Thunderstorms More severe ReasonableGreater risks due to heavy rain, hail, storm gusts
Lightning Much more frequentlyGood Increased damage
Tornadoes More frequent Low Increased damage
Storm surges Up to 20 cm higher Good Greater threat to the North Sea coast
Ozone layer Greatest thinning out around 2010; very slow recovery since Good Higher long-term exposure to UV radiation, higher risk of skin diseases
Extra tropical (winter) storms Tendency for more violent, but possibly fewer, storms following different tracks* Uncertain Considerable risk of damages

Turbidity,

Aerosols

Uncertain Uncertain

* A recent research project on changes in extreme air temperatures, precipitation and wind speeds in which the DWD took part shows an increasing propensity for winter storms in the future; there is no evidence that such storms will be of greater intensity, however.

All areas of society, policy and business will be affected by these, in many cases quite momentous, changes. For example, higher temperatures and more frequent and longer periods of extreme heat pose a growing risk for human health and can result in large numbers of deaths in our country as well (as we experienced in the summer of 2003). Higher temperatures also mean that less energy is needed for heating purposes and more for cooling.
Changed temperatures have numerous different effects on agriculture: earlier onset of plant growth and longer growing seasons; thermophilic species can be cultivated (e.g. in viticulture), etc. In some health resorts, increased heat stress could cause an increasing range of problems.
Our leisure activities will also be influenced: winter sports will no longer be possible on the same scale as today; people will be able to use their gardens from much earlier in spring for much longer into later autumn; etc.
But that's not all: our immediate environment will change, too. The urban heat island effect will become stronger, with some homes so hot during the day that they can no longer cool down sufficiently overnight, and many more effects. This will be compounded by the impact of changing precipitation and other weather elements. It is reasonable to assume that not all the consequences of these changes are foreseeable.

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Detailed modelling of climate impacts

These few examples show how real climate change already is and how much it has - and will increasingly – become part of our experience. We must not only direct our efforts on mitigation, but also on adapting to the consequences of climate change. The task now is to precisely assess the effects of climate change and get ourselves prepared for adaptation. The Deutscher Wetterdienst took the initiative for this very early on. Our recognised heat warning and pollen forecasts services are in great demand throughout Germany and internationally. Both are freely available on the DWD's website.

Von der Messung bis zur Beratung - schematische Darstellung der Klimaservices des DWD unter Berücksichtigung des Klimawandels


The Deutscher Wetterdienst is also working on a detailed model of climate change. Our aim is to project and present the impacts of climate change on various aspects of our life in a way which provides policymakers, public authorities, architects and doctors as well as business and industry with the information they need for their work.

The DWD has several decades of experience in advising decision-makers at the federal, state and local authority levels, as well as the private sector, on the climatological issues which are relevant to planning. These include projects for transport development and town planning, as well as water management, agricultural, health sector and technical climatology – in particular, concerning the use of renewable energies. In the past, advice was given on the basis of long-term weather observations and measurements. Now, our advice also relies on the results of climate scenarios and climate forecast models. These are not only the product of many global climate models, but also of the information provided by regional climate models at much higher levels of  spatial resolution for Germany. The Deutscher Wetterdienst does not draw on just one, but on several regional climate models.

The Deutscher Wetterdienst provides advice and prepares expert reports by drawing on a selection of available regional climate models and using these together with impact models. A few examples are:

In the field of urban planning, the DWD uses the high resolution MUKLIMO-3 urban climate model to identify the distribution of wind and air temperatures in built-up areas and their environs. Combined with statistical procedures, this model enables an objectively accurate evaluation to be made of the urban climate in various parts of the town for a wide variety of climate scenarios. It is already clear that fresh air lanes and green spaces will grow in importance in the future. Architects will have to develop new building concepts – such as ensuring that footpaths are shaded from the summer sun. Another approach is to begin to make greater use of building materials which stop buildings heating up in the summer.

Climate scenario calculations are combined with the DWD's AMBER model system for agriculture. AMBER includes programmes on crop and soil climate as well as agricultural input management (dealing with fertilisation and irrigation, the treatment of plant diseases and pests).

A third example is the DWD's SNOW model. As well as surface run off, this model also calculates the development of snow cover and its water equivalent on the basis of precipitation and snow melt and consequently improves forecasting of the strength and frequency of future flood situations.

The objective in all these cases is to be able to assess what impact climate change has on people and the human environment.

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Actively responding to climate change

In summary, climate change does not manifest itself in numbers alone. In fact, climate change involves highly differentiated changes in a whole range of different meteorological elements. These changes also vary starkly from place to place and across time. Specialists need

·  a broad database,

· large computer systems

·  and a great deal of expertise

to be able to determine – as early and as accurately as possible – how the climate has already changed and what we may expect in the future. Only on the basis of this information – to which the Deutscher Wetterdienst is a major contributor – will our society be able to counteract undesirable climatic trends and to develop and implement successful adaptation measures.

The global climate train – over which we as humans also have some control – has already left the station. It is unstoppable. But, all the same, we are still able to observe exactly the journey we have set off on and draw conclusions and give advice on what is happening around us. If all those with responsibility combine their efforts we will be able to influence the speed of travel and, perhaps, bring the train into a safe station. Let's make the most of this opportunity.

Contact: Dr Paul Becker

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