How does the sea temperature affect the weather?

Climate change

Hanna Hüging

born 1985; Studied Geography (BA) and Environmental Science (MSc); currently research assistant in the research group "Energy, Transport and Climate Policy" at the Wuppertal Institute. Main focus of work at the moment: climate protection and energy efficiency in transport.

What influences our climate today and in the past

"A swallow doesn't make a summer" and a hot summer does not necessarily mean climate change. However, weather and climate are closely related and are shaped by complex interactions in the earth's climate system.

A hot summer doesn't necessarily mean climate change. (& copy picture-alliance / dpa)

The relationship between weather and climate

Weather is the short-term state of the atmosphere in a specific place at a specific time. So whether the sun is shining, whether it is raining, whether it is cold or warm, where the wind comes from. Over time, the weather in one place varies a lot. The climate, on the other hand, relates to longer periods of time - at least 30 years. Typical conditions are derived from a large number of weather observations. This enables the climate of a region to be determined. The climate not only represents the average weather conditions, but also describes the probabilities of extreme events and deviations from the mean.

One can imagine the connection using a cube. The weather is the side of the cube that is currently on top. The climate, on the other hand, describes how often each of the six sides is rolled on average and the probability that the same side is up three times, for example. If the example is transferred to the term climate change, this describes a change in the statistical parameters, for example through a marked dice. A single weather event is therefore not a sign of climate change, because only in the context of long observation periods can it be determined whether climate changes have taken place. The record summer of 2003, for example, cannot be seen solely as an indication of changes in the climate, but many exceptionally warm summers can show that there has been a change in the statistical parameters and thus in the climate.

What influences the climate on earth?

The earth's climate is determined by complex, interactive processes on earth as well as by external factors, the sun being the most important of these factors - it provides the energy for our climate system. The atmosphere, which surrounds the earth as a gaseous shell, is predominantly permeable to the incoming solar radiation as short-wave radiation, which we perceive as light, among other things. Around 30 percent of the incident radiation, however, is already reflected in the atmosphere or on the earth's surface and goes back into space without affecting the climate system. This reflexivity - called albedo - on the earth's surface is highest in snow and ice regions.

In addition to gases and clouds, the atmosphere also consists of small particles such as dust or soot - so-called aerosols - that influence how much radiation is reflected. The remaining solar radiation is absorbed by the atmosphere and the earth's surface, which increases the temperature and thus leads to a stronger radiation of heat from the earth's surface into the atmosphere. If this thermal radiation left the earth unhindered, the global average temperature would be -18 ° C.

The natural greenhouse gas effect

We owe the fact that the average temperature on earth is + 15 ° C to the natural greenhouse gas effect. This means that only part of the long-wave heat radiation can leave the atmosphere and the majority is absorbed and partly reflected back to the earth, which has a warming effect on the earth's surface and the deeper layers of the atmosphere.

A greenhouse works in a very similar way. The glass roof is permeable to short-wave solar radiation, but not to long-wave thermal radiation, so that the inside of the greenhouse is warmed up. So-called greenhouse gases take on the role of the glass roof in the atmosphere. Water vapor and carbon dioxide (CO2) are the most important greenhouse gases. In addition, methane (CH4), Nitrogen oxides (NOx), Ozone (O3) and other gases in the atmosphere have a greenhouse gas effect. Overall, however, greenhouse gases only make up a very small part of our atmosphere. About 99 percent of the atmosphere consists of nitrogen and oxygen, which have no greenhouse gas effects. If you change the concentration of greenhouse gases in the atmosphere, the greenhouse gas effect also changes and has an impact on temperatures and the entire climate system of the earth.

Fig.1: The natural greenhouse effect. Source: Allianz Umweltstiftung, information on the topic of climate (© Allianz Umweltstiftung) (& copy Allianz Umweltstiftung)

Interactions within the climate system

Different components together form the earth's climate system. The atmosphere is the main component. It influences how much energy enters the climate system in the form of short-wave solar radiation or long-wave thermal radiation. Further components of the climate system are: The hydrosphere, consisting of the oceans and water in lakes, rivers or clouds. The cryosphere, which includes all forms of ice (e.g. glaciers, sea ice). The biosphere, which consists of the entirety of animals and plants, as well as the pedosphere and the lithosphere, which comprise the earth and the rock below.

The various components are connected by energy and material flows and the interactions between them have an impact on our climate. For example, the biosphere binds CO through the build-up of biomass2 and thus has an impact on the concentration of this greenhouse gas in the atmosphere. Since snow and ice (cryosphere) are highly reflective, the size of these surfaces affects the reflection of solar radiation. There is a positive feedback mechanism, which means that a change in the climate is intensified by this connection: the warmer it is on earth, the more snow and ice melts, the lower the reflection of solar radiation and the higher the temperatures rise on the Earth.

The processes of the hydrosphere are very closely connected to the atmosphere and have a particularly high impact on our climate. Oceans store and transport heat, which leads to regional temperature differences. The climate in Europe, for example, is largely determined by the warming Gulf Stream. In the atmosphere, water in the form of clouds or water vapor has a decisive influence on how much solar radiation is reflected (clouds) and how permeable the atmosphere is for long-wave heat radiation (water vapor).

The soil (pedosphere) has an influence on the reflexivity of the earth's surface through its color or its vegetation. In addition, soils are connected to the atmosphere through material cycles such as the carbon cycle. Changes in soil properties such as the drainage of moors or the thawing of soils that were originally frozen all year round (permafrost soils) can cause large amounts of CO2 and release methane. Even with the weathering of rock (lithosphere), CO2 released from the earth's crust.

Our climate on earth is consequently a very complex system and any intervention in this system can cause a series of changes, the complexity and extent of which are hardly predictable.

Fig. 2: Schematic representation of the climate system (source Wuppertal Institute)

Past climate changes

The climate has changed numerous times over the course of 4.6 billion years of Earth's history. After very warm phases came long ice ages, which in turn were replaced by warm periods. At the time of the dinosaurs in the Mesozoic (approx. 251 to 65.5 million years before our time) the global average temperature was approx. Six to eight degrees higher and there was a warm, tropical climate. The sea level was about 80 meters higher than today, although the continents and oceans were distributed differently. It was only around two million years ago that the continents and oceans formed as they are known to us in their current form. Since then, the climate has been characterized by cyclically recurring ice cycles.

The temperature profile of the last 400,000 years shows a change between long ice ages and the subsequent warm periods. Since the end of the last ice age 15,000 years ago, global temperatures have slowly warmed by 5 degrees Celsius over a period of around 5,000 years. Since then we have been in a warm period with relatively stable temperatures. The human-induced climate change threatens to bring about a similarly strong rise in temperature over a much shorter period of time - within a hundred years. The next ice age would not be expected for 30,000 to 50,000 years.

Causes of Natural Climate Change

The climate changes in the past have various causes and, in addition to triggers, feedback effects have a major influence. Various changes in the Earth's radiation budget can trigger or intensify a climate change:

  1. a change in the incident solar radiation, e.g. due to changes in the distance between the sun and the earth or the activity of the sun;

  2. a change in the proportion of reflected solar radiation, e.g. due to a change in the reflectivity of the atmosphere or the earth's surface;

  3. a change in the heat radiation emitted by the earth, e.g. by changing the greenhouse gas concentration.
For example, the warm climate at the time of the dinosaurs was extremely high in CO2 Concentration connected (cf. 3), which had been released by magma outflow. The greenhouse effect was particularly high at that time. The end of most of the species living at the time was probably triggered by a meteorite impact, which brought huge amounts of dust into the atmosphere, so that significantly less solar radiation reached the earth (see 2). Similar short-term effects can be observed after volcanic eruptions.

The ice age cycles are related to the change in the earth's orbit around the sun. The so-called Milankowitch-Zkylen change the amount of solar radiation (cf. 1), which the different latitudes reach seasonally. As a result, masses of ice and snow can spread and trigger further cooling due to the increased reflection (cf. 2).

Figure 3: Course of the temperature (red) in the Antarctic and the CO2 concentration (blue) over the past 650,000 years. The parallel curve shows the relationship between temperature change and greenhouse gas concentration (source: IPCC (2007), based on: Latif, M. (2007): How strong is anthropogenic climate change ?, in: Müller, M., U. Fuentes / H . Kohl (Ed .: The UN World Climate Report. Reports on a halting catastrophe. Kiepenheuer and Witsch, Cologne., Pp. 186-189.

Samples from Antarctic ice cores have shown that temperature and CO2-Concentration of the atmosphere during the past Ice Age cycles strongly correlate (Figure 3). Even if the causes of the CO2Fluctuations during the Ice Age cycles have not yet been fully clarified, but it is known that the CO2-Concentration has significantly influenced climate fluctuations. This knowledge can be used to make predictions for the future.

Past climate changes show that the climate system on earth is a very sensitive system and how much CO2-Concentration and global average temperatures depend on each other.

literature

IPCC 2007: Frequently Asked Questions and Answers. In: Climate Change 2007: Scientific Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller, Eds., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. German translation by the German IPCC coordination office, Bonn, 2011.

Latif, Mojib (2007): Are we getting the climate out of sync? Background and forecasts, Fischer Taschbuch Verlag, Frankfurt am Main.

Rahmstorf, Stefan and Schellnhuber, Hand Joachim (2007): Climate change - diagnosis, prognoses, therapy 6th edition, C. H. Beck, Munich.