Thermal Expansion Of Seawater Research Articles

Analysis of Global Sea Level Change Based on Multi-Source Data

Global sea level rise is both a major indicator and consequence of global warming. At present, global warming is causing sea level rise in two main ways: one is the thermal expansion of sea water, and the other is the injection of large amounts of fresh water into the ocean after glaciers and ice sheets melt. In this paper, satellite altimeter data are used to study the total changes of global sea level from 2002 to 2020. Different from most previous studies, this study proposes a calculation method of sea level anomaly using only the along track altimetry data, which is similar to considering the satellite points as tide gauges, in order to avoid the error caused by interpolation in the map data. In addition, GRACE satellite data are used to calculate the changes of global sea level caused by water increase; temperature and salinity data are used to calculate the changes from ocean thermal expansion. Next, using satellite altimetry data, the calculation results show that the global sea level rise rate in the period of 2002–2020 is 3.3 mm/a. During this period, the sea level change caused by the increase of sea water calculated with GRACE satellite data is 2.07 mm/a, and that caused by the thermal expansion of seawater is 0.62 mm/a. The sea level rise caused by the increase of water volume accounts for 62.7% of the total sea level rise.

Climate and ocean circulation in the aftermath of a Marinoan snowball Earth

Abstract. When a snowball Earth deglaciates through a very high atmospheric CO2 concentration, the resulting inflow of freshwater leads to a stably stratified ocean, and the strong greenhouse conditions drive the climate into a very warm state. Here, we use a coupled atmosphere–ocean general circulation model, applying different scenarios for the evolution of atmospheric CO2, to conduct the first simulation of the climate and the three-dimensional ocean circulation in the aftermath of the Marinoan snowball Earth. The simulations show that the strong freshwater stratification breaks up on a timescale of the order of 103 years, mostly independent of the applied CO2 scenario. This is driven by the upwelling of salty waters in high latitudes, mainly the Northern Hemisphere, where a strong circumpolar current dominates the circulation. In the warmest CO2 scenario, the simulated Marinoan supergreenhouse climate reaches a global mean surface temperature of about 30 ∘C under an atmospheric CO2 concentration of 15×103 parts per million by volume, which is a moderate temperature compared to previous estimates. Consequently, the thermal expansion of seawater causes a sea-level rise of only 8 m, with most of it occurring during the first 3000 years. Our results imply that the surface temperatures of that time were potentially not as threatening for early metazoa as previously assumed. Furthermore, the short destratification timescale found in this study implies that Marinoan cap dolostones accumulated during the deglacial period, given that they were deposited under the influence of a freshwater environment.

Kinematics of global mean thermosteric sea level during 1993–2019

Abstract Because oceans cover 71% of Earth’s surface, ocean warming, consequential for thermal expansion of sea water, has been the largest contributor to the global mean sea level rise averaged over the 20 th and the early 21 st century. This study first generates quasi-observed monthly globally averaged thermosteric sea level time series by removing the contributions of global mean sea level budget components, namely, Glaciers, Greenland, Antarctica, and Terrestrial Water Storage from satellite altimetry measured global sea level changes during 1993–2019. A baseline kinematic model with global mean thermosteric sea level trend and a uniform acceleration is solved to evaluate the performance of a rigorous mixed kinematic model. The model also includes coefficients of monthly lagged 60 yearlong cumulative global mean sea surface temperature gradients and control variables of lunisolar origins and representations for first order autoregressive disturbances. The mixed kinematic model explains 94% (Adjusted R 2)1 of the total variability in quasi-observed monthly and globally averaged thermosteric time series compared to the 46% of the baseline kinematic model’s Adjusted R 2. The estimated trend, 1.19±0.03 mm/yr., is attributed to the long-term ocean warming. Whereas eleven statistically significant (α = 0.05) monthly lagged cumulative global mean sea surface temperature gradients each having a memory of 60 years explain the remainder transient global mean thermosteric sea level changes due to the episodic ocean surface warming and cooling during this period. The series also exhibit signatures of a statistically significant contingent uniform global sea level acceleration and periodic lunisolar forcings.

Sea-level rise in Denmark: Bridging local reconstructions and global projections

Between 1850 and 2006 global mean sea level rose by 24 ± 18 cm. It is projected to rise a further 52 ± 21 cm under the Representative Concentration Pathway (RCP) 4.5 scenario, which approximates the carbon emissions reductions of the ‘Paris Agreement’ climate pathway. It is projected to rise 74 ± 28 cm under the RCP8.5 scenario, which represents a ‘business-as-usual’ climate pathway (Box & Colgan 2017). These rates of recent and future sea-level rise are faster than those reconstructed for previous warm intervals, such as the Medieval Climatic Optimum (c. 1000 to 1400 CE) and the Holocene Thermal Maximum (c. 7000 to 3000 BCE) (Gehrels & Shennan 2015). Moreover, palaeo reconstructions indicate a global sea-level sensitivity of two metres per degree of warming (Levermann et al. 2013).
 The forces driving global sea-level change are complex. The global sea-level budget includes the transfer of land ice into the ocean, thermal expansion of seawater, changes in land water storage, and changes in ocean basin volume (Church et al. 2013). At the local scale, the evolving planetary gravity due to shifting water and ice masses, shifting oceanic and atmospheric currents and persistent tectonic and glacial isostatic adjustment processes can also be important. Sea-level changes around the globe are therefore far from uniform (Jevrejeva et al. 2016).
 Here, we highlight the value of combining palaeo reconstructions of sea level, the measured tide gauge record, and projections of future sea level. This allows us to understand local sea-level changes from the recent past in the context of global projections for the near future (0 to 2100 CE). We explore the strong differences in local sea-level histories and future projections at three Danish cities: Skagen and Esbjerg, as they have contrasting glacio-isostatic adjustment histories, and Copenhagen, where we also compare local and global drivers of present-day sea-level rise based on previously published research.

한반도의 해수면 상승을 고려한 설계조위 산정에 관한 연구

이산화탄소의 배출 증가와 지구온난화, 엘리뇨 현상, 라니냐 현상 등과 같은 이상기후 현상의 발생빈도 증가로 인하여 전 세계적으로 내륙과 해안의 온도가 상승하고 있다. 지구온난화로 인한 바닷물의 열팽창 그리고 빙하의 해빙 등으로 인한 지구의 해수면은 매년 2.0mm/yr(전 세계 평균값)의 속도로 상승하고 있다. 그러나 해안에 인접한 수리구조물 혹은 해안 수리구조물을 설계할 시 기준이 되는 설계조위는 과거 관측된 조위 값으로부터 4대 분조 및 조화상수를 분석하거나 수치모형 실험에 의해 결정된다. 따라서, 설계조위는 구조물의 설계빈도에 상응하는 해수면의 상승속도를 감안해야 할 필요가 있다고 사료된다. 본 연구에서는 국립해양조사원(Korea Hydrographic and Oceanographic Administration; KHOA)에서 운영하고 있는 46개소의 조위관측소를 대상으로 관측개시일부터 2015년까지 시단위로 조위자료를 수집하였다. 우리나라를 크게 남해동부, 남해서부, 동해남부, 동해중부, 서해남부, 서해중부, 제주로 총 7개의 해역으로 구분하여 월별, 연별 변동추이 및 연평균 상승률 분석을 수행하였다. 향후 국지적 해수면상승의 원인규명 및 설계조위 고려 시 기초자료로 활용가능 할 것으로 판단된다. The air temperatures of the coast and inland are rising due to an increase in carbon dioxide emissions and abnormal climate phenomena caused by global warming, El Nino, La Nina and so on. The sea levels of the Earth are rising by approximately 2.0 mm per year (global average value) due to the thermal expansion of sea water, melting of glaciers and other causes by global warming. On the other hand, when it comes to designing a hydraulic structure or coastal hydraulic structure, the standard of the design water level is decided by analyzing four largeness tide values and a harmonic constant with the observed tidal water level or simulating numerical model. Therefore, the design tidal water level needs to consider an increasing speed of the seawater level, which corresponds to the design frequency. In the present study, the observed tidal water levels targeting 46 tidal stations operated by the Korea Hydrographic and Oceanographic Administration (KHOA) from the beginning of observations to 2015 per hour were collected. The variation of the monthly and yearly and increasing ratio were performed and divided into 7 seas, such as east and west part of the Southern Sea, south part and middle of the East Sea, south part and middle of the Western Sea, and Jeju Sea. The current study could be used to determine the cause of local seawater rises and reflect the design tidal water level as basic data.

해수면 상승을 고려한 하천 외수위 결정에 관한 연구

The sea level of the Earth is rising approximately 2.0mm per year (global average value) due to thermal expansion of sea water, melting of glaciers and other causes by global warming. However, when it comes to design a river, the standard of design water level is decided by analyzing four largeness tide value and harmonic constant with observed tidal water level. Therefore, it seems the external water level needs to consider an increasing speed of the seawater level which corresponds to a design frequency. In the present study, the hourly observed tidal water level targeting 47 tidal stations operated by Korea Hydrographic and Oceanographic Administration (KHOA) from beginning of observation to 2015 per hour has been collected. The variation of monthly and yearly and increasing ratio have been performed divided 4 seas such as the Southern, East, Western, and Jeju Sea. Also, the external water level existing design for rivers nearby a coast was been reviewed. The current study could be used to figure out the cause of local seawater rise and reflect the external water level as basic data.

Sea Level Rise and Coastal Vulnerability along the Eastern Coast of India through Geo-spatial Technologies

The study emphasizes the local and regional level coastal vulnerability in the context of climate change induced present sea level rise using Sea level and tidal gauge data and advanced geo spatial technologies along the eastern coast of India. The coast is a potential hot spot zone were found the immediate effect of sea level rise. Presently climate change induced global warming and the melting of ice sheets and continental glaciers continually increase the sea level, which leads the natural hazards such as Tsunami, storm surges, thermal expansion of sea water and cyclones. The study was used SRTM global DEM with 90 m resolution to derive the coastal elevation, inundation risk zones along the eastern coast of India. The sea level rise scenario has been explained by using a 5th order polynomial curve which also interpolates and extrapolate the gaps within the available data of four tidal gauge stations. The results show that northern portion (Ganga-Brahmaputra delta region) of the coast, mostly affected by the sea level rise (4.7 mm per year) where the Sundarban region is the most vulnerable region due to the lower elevation (ranges 0 to 20 m) and higher tidal influence. Also Visakhapatnam and Bhubaneswar have a higher rate of sea level rise respectively 0.73 and 0.43 which increase the erosional activity and probable inundation level. As this study reveals the level of vulnerability, it helps to develop mitigation and adaptation measures in those most vulnerable areas to sea level rise problems. The final results support and suggests planners and decision makers in the spatial identification for the future strategies.

Complementing thermosteric sea level rise estimates

Abstract. Thermal expansion of seawater has been one of the most important contributors to global sea level rise (SLR) over the past 100 years. Yet, observational estimates of this volumetric response of the world's oceans to temperature changes are sparse and mostly limited to the ocean's upper 700 m. Furthermore, only a part of the available climate model data is sufficiently diagnosed to complete our quantitative understanding of thermosteric SLR (thSLR). Here, we extend the available set of thSLR diagnostics from the Coupled Model Intercomparison Project Phase 5 (CMIP5), analyze those model results in order to complement upper-ocean observations and enable the development of surrogate techniques to project thSLR using vertical temperature profile and ocean heat uptake time series. Specifically, based on CMIP5 temperature and salinity data, we provide a compilation of thermal expansion time series that comprise 30 % more simulations than currently published within CMIP5. We find that 21st century thSLR estimates derived solely based on observational estimates from the upper 700 m (2000 m) would have to be multiplied by a factor of 1.39 (1.17) with 90 % uncertainty ranges of 1.24 to 1.58 (1.05 to 1.31) in order to account for thSLR contributions from deeper levels. Half (50 %) of the multi-model total expansion originates from depths below 490 ± 90 m, with the range indicating scenario-to-scenario variations. To support the development of surrogate methods to project thermal expansion, we calibrate two simplified parameterizations against CMIP5 estimates of thSLR: one parameterization is suitable for scenarios where hemispheric ocean temperature profiles are available, the other, where only the total ocean heat uptake is known (goodness of fit: ±5 and ±9 %, respectively).

Sources of 21st century regional sea-level rise along the coast of northwest Europe

Abstract. Changes in both global and regional mean sea level, and changes in the magnitude of extreme flood heights, are the result of a combination of several distinct contributions most, but not all, of which are associated with climate change. These contributions include effects in the solid earth, gravity field, changes in ocean mass due to ice loss from ice sheets and glaciers, thermal expansion, alterations in ocean circulation driven by climate change and changing freshwater fluxes, and the intensity of storm surges. Due to the diverse range of models required to simulate these systems, the contributions to sea-level change have usually been discussed in isolation rather than in one self-consistent assessment. Focusing on the coastline of northwest Europe, we consider all the processes mentioned above and their relative impact on 21st century regional mean sea levels and the 50-year return flood height. As far as possible our projections of change are derived from process-based models forced by the A1B emissions scenario to provide a self-consistent comparison of the contributions. We address uncertainty by considering both a mid-range and an illustrative high-end combination of the different components. For our mid-range ice loss scenario we find that thermal expansion of seawater is the dominant contributor to change in northwest European sea level by 2100. However, the projected contribution to extreme sea level, due to changes in storminess alone, is in some places significant and comparable to the global mean contribution of thermal expansion. For example, under the A1B emissions scenario, by 2100, change in storminess contributes around 15 cm to the increase in projected height of the 50-year storm surge on the west coast of the Jutland Peninsula, compared with a contribution of around 22 cm due to thermal expansion and a total of 58 cm from all of the contributions we consider. An illustrative combination of our high-end projections suggests increases in the 50-year return level of 86 cm at Sheerness, 95 cm at Roscoff, 106 cm at Esbjerg, and 67cm at Bergen. The notable regional differences between these locations arise primarily from differences in the rates of vertical land movement and changes in storminess.

Scientific Discourse: Climate Change and Sea-Level Rise

AbstractSea-level rise (SLR) is one of the most damaging impacts of climate change. Rising sea levels lead to loss of coastal wetlands, coastal flooding, degradation of coastal ecosystems, and a general loss of quality of life. Due to its potential impacts on coastal management and on population health and safety, the impact of climate change on SLR has drawn significant attention in recent literature. SLR is associated with processes including glacial activity, ice-sheet melting, thermal expansion of sea water, hydrologic events such as increased or decreased land-based discharges, and local effects such as El Nino and La Nina, all of which are complexly linked to changes in global temperature. Unfortunately, many of these physical processes are not well understood in their relation to climate change, and the scientific knowledge required to represent them fully in predictive analysis is so complex that many current studies are shifting away from physical climate models to the application of empirical, s...

Models find large natural variability in future regional sea level rise

Melting glaciers, ice caps, and ice sheets and thermal expansion of seawater, along with groundwater depletion, have already caused the global ocean to rise at a rate of 1.8 centimeters per decade over the past century. In recent decades the pace has climbed to 3.1 centimeters per decade. As the atmospheric greenhouse gas concentration continues to rise, so will the oceans.

The Reversibility of Sea Level Rise

Abstract During the last century, global climate has been warming, and projections indicate that such a warming is likely to continue over coming decades. Most of the extra heat is stored in the ocean, resulting in thermal expansion of seawater and global mean sea level rise. Previous studies have shown that after CO2 emissions cease or CO2 concentration is stabilized, global mean surface air temperature stabilizes or decreases slowly, but sea level continues to rise. Using idealized CO2 scenario simulations with a hierarchy of models including an AOGCM and a step-response model, the authors show how the evolution of thermal expansion can be interpreted in terms of the climate energy balance and the vertical profile of ocean warming. Whereas surface temperature depends on cumulative CO2 emissions, sea level rise due to thermal expansion depends on the time profile of emissions. Sea level rise is smaller for later emissions, implying that targets to limit sea level rise would need to refer to the rate of emissions, not only to the time integral. Thermal expansion is in principle reversible, but to halt or reverse it quickly requires the radiative forcing to be reduced substantially, which is possible on centennial time scales only by geoengineering. If it could be done, the results indicate that heat would leave the ocean more readily than it entered, but even if thermal expansion were returned to zero, the geographical pattern of sea level would be altered. Therefore, despite any aggressive CO2 mitigation, regional sea level change is inevitable.

Foraminiferal assemblages response to anthropogenic influence and parallel to decadal sea-level changes over the last 70 years in Lake Kugushi, Fukui Prefecture, southwest Japan

Foraminiferal assemblages in Lake Kugushi in the Sea of Japan coast of Southwest Japan responded to both human activity and sea-level changes over the last 70 years. Human modifications in and around this lake were mainly related to the dredging and widening of the Urami River in 1935 and to shore protection projects that removed aquatic plants around the lake in the middle 1970s. About 60% of the natural shoreline was replaced by artificial ones. Marine foraminifera migrated into the southern part of the lake after the modifications of 1935. Brackish foraminifera preferring phytodetritus became dominant from the middle 1970s, while the original assemblage, preferring low-salinity and probably land-derived organic matter, decreased. The sea-level rise over the last 70 years is clearly indicated by two kinds of foraminiferal assemblages: the appearance of marine species in the 1950s and 1970s, and the development of a brackish assemblage preferring eutrophic water from the 1980s onward. The latter is an assemblage dominated by Trochammina hadai, which is common in coastal lagoons with a well developed halocline and highly eutrophied argillaceous substrates. Based on the different response of these foraminiferal assemblages to sea-level rise, the most recent sea-level rise is driven by a mechanism unlike those in the 1970s and 1950s. The thermal expansion of seawater will lead to coastal lagoons that will be more stagnant and eutrophic, with little exchange of coastal marine water.

Climate Change in Australia to the year 2030 AD

Atmospheric scientists predict significant global climate changes as a result of increasing levels of greenhouse gases in the atmosphere. The consequences of such changes in the energy budget of the atmosphere on regionally-specific climate changes is difficult to predict. The scenario presented is a plausible future climate for the Australian region, made solely for the purpose of examining the type and magnitude of likely impacts of such changes. While the predicted changes in the gross features of global change are regarded as highly probable, the regional changes suggested in this scenario are most speculative. The scenario deals only with the primary factors of climate such as temperature, rainfall, etc. No attempt is made to predict regional changes in secondary climate factors such as evaporation, soil moisture, etc., where the interaction of two or more primary factors is involved. Predicting sea level rises is equally difficult. It is assumed that future rises will be in proportion to temperature changes with the proportionally based on previously observed changes. These rises are thought to be due to thermal expansion of sea water and possibly also to partial melting of mountain glaciers and the fringes of the high-latitude ice caps.

Eustatic variations during the Paleocene‐Eocene greenhouse world

We reconstruct eustatic variations during the latest Paleocene and earliest Eocene (∼58–52 Ma). Dinoflagellate cysts, grain size fractions, and organic biomarkers in marine sections at four sites from three continents indicate an increased distance to the coast during the Paleocene‐Eocene thermal maximum (PETM). The same trend is recognized in published records from other sites around the world. Together, the data indicate a eustatic rise during the PETM, beginning 20 to 200 ka before the globally recorded negative carbon isotope excursion (CIE) at ∼55.5 Ma. Although correlations are tentative, we recognize other global transgressions during Chrons C25n and C24n. The latter may be associated with Eocene Thermal Maximum 2 (∼53.5 Ma) or the “X”‐event (∼52 Ma). These results suggest a link between global sea level and “hyperthermal” intervals, potentially because of the melting of small alpine ice sheets on Antarctica, thermal expansion of seawater, or both. However, the early onset of sea level rise relative to the CIE of the PETM suggests contributions from other mechanisms, perhaps decreasing ocean basin volume, on sea level rise.

Climate Change Projections for the Twenty-First Century and Climate Change Commitment in the CCSM3

Abstract Climate change scenario simulations with the Community Climate System Model version 3 (CCSM3), a global coupled climate model, show that if concentrations of all greenhouse gases (GHGs) could have been stabilized at the year 2000, the climate system would already be committed to 0.4°C more warming by the end of the twenty-first century. Committed sea level rise by 2100 is about an order of magnitude more, percentage-wise, compared to sea level rise simulated in the twentieth century. This increase in the model is produced only by thermal expansion of seawater, and does not take into account melt from ice sheets and glaciers, which could at least double that number. Several tenths of a degree of additional warming occurs in the model for the next 200 yr in the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) B1 and A1B scenarios after stabilization in the year 2100, but with twice as much sea level rise after 100 yr, and doubling yet again in the next 100 yr to 2300. At the end of the twenty-first century, the warming in the tropical Pacific for the A2, A1B, and B1 scenarios resembles an El Niño–like response, likely due to cloud feedbacks in the model as shown in an earlier version. Greatest warming occurs at high northern latitudes and over continents. The monsoon regimes intensify somewhat in the future warmer climate, with decreases of sea level pressure at high latitudes and increases in the subtropics and parts of the midlatitudes. There is a weak summer midlatitude soil moisture drying in this model as documented in previous models. Sea ice distributions in both hemispheres are somewhat overextensive, but with about the right ice thickness at the end of the twentieth century. Future decreases in sea ice with global warming are proportional to the temperature response from the forcing scenarios, with the high forcing scenario, A2, producing an ice-free Arctic in summer by the year 2100.

Rates and causes of recent global sea-level rise inferred from long tide gauge data records

Tide gauge data at seven sites of the Permanent Service for Mean Sea Level (PSMSL), with information for relative sea-level during the past 140–200 yr, were analyzed to examine the rates and causes of the global sea-level rise (GSLR) during the twentieth century. By subtracting linear trends for relative sea-level rise during the past 100 yr from the observed data, we get the apparent GSLRs of ∼1 mm yr −1 for five sites around the Baltic Sea and Brest. The rate for San Francisco is significantly larger than this, with an optimum value ∼2 mm yr −1. The spatial difference of ∼1 mm yr −1 between these sites is reasonably explained by the recent melting of the Greenland ice sheet with an equivalent sea-level rise of ∼1 mm yr −1. The predicted relative sea-level change for this melting scenario is 0.5 mm yr −1 at sites around the Baltic Sea and Brest, and 1.5 mm yr −1 for San Francisco. The residuals between observations and predictions, ∼0.5 mm yr −1 at all sites, may be contributed by thermal expansion of seawater and/or other melting sources. These results suggest the rate of twentieth-century GSLR to be 1.5 mm yr −1.

Comparison of results from several AOGCMs for global and regional sea-level change 1900-2100

Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need for detailed analysis and intercomparison in order to understand and reduce the disagreements.

A Possible Change in Mass Balance of Greenland and Antarctic Ice Sheets in the Coming Century

A high-resolution GCM is found to simulate precipitation and surface energy balance of high latitudes with high accuracy. This opens new possibilities to investigate the future mass balance of polar glaciers and its effect on sea level. The surface mass balance of the Greenland and the Antarctic ice sheets is simulated using the ECHAM3 GCM with TI06 horizontal resolution. With this model, two 5-year integrations for the present and doubled carbon dioxide conditions based on the boundary conditions provided by the ECHAM1/T21 transient experiment have been conducted. A comparison of the two experiments over Greenland and Antarctica shows to what extent the effect of climate change on the mass balance on the two largest glaciers of the world can differ. On Greenland one sees a slight decrease in accumulation and a substantial increase in melt, while on Antarctica a large increase in accumulation without melt is projected. Translating the mass balances into terms of sea-level equivalent. the Greenland discharge causes a sea level rise of 1. 1 mm yr−1, while the accumulation on Antarctica tends to lower it by 0.9 mm yr−1. The change in the combined mass balance of the two continents is almost zero. The sea level change of the next century can be affected more effectively by the thermal expansion of seawater and the mass balance of smaller glaciers outside of Greenland and Antarctica.

Climate of the 21st century

The outgoing long wave radiation to space is significantly reduced as a result of heat absorption by the so-called greenhouse gases, notably water vapour, carbon dioxide, methane, nitrous oxides and chlorofluorocarbons. The dominating ones are water vapour and carbon dioxide. The direct effect of the greenhouse gases is to increase the average temperature of the earth's surface by some 33°C, that is from −18°C to the present +15°C. Since the industrial revolution the combustion of fossil fuels and deforestation has led to an increase of 26% in carbon dioxide in the atmosphere. It is presently increasing by about 0.5% per year. Based on strict radiative forcing calculations, the total additional warming because of the increase in greenhouse gases, not including the effect of associated changes in water vapour, is equivalent to about 2.5 W m −2 and is estimated to increase to some 10 W m −2 at the end of the next century. The solar constant, by comparison, is equal to 341 W m −2 globally averaged. The effect on climate cannot satisfactorily be estimated on radiation balance calculation only but must incorporate the large scale atmospheric circulation and the important feedbacks with water vapour (positive feedback), clouds (both positive and negative feedbacks), surface albedo and the oceans. For that reason it is necessary to build comprehensive mathematical models of the coupled ocean/land atmosphere system and carry out numerical simulation experiments. Several such studies have been undertaken during the last few years both in Europe and the USA. Results from these experiments, and in particular from those carried out at the Max-Planck-Institut für Meteorologie in Hamburg, will be presented and discussed. Because of the enormous complexity of the problem, a number of simplified assumptions have been used and the results so far must be cautiously assessed. The overall global warming from these experiments is about 3°C with a difference of about 0.5°C between the experiments. There are large regional differences and the warming is generally larger over land than over sea. A particular problem is the temperature of the North Atlantic and also in the Antarctic waters where changes in the deep ocean circulation are significant. The strong coupling to the deep ocean circulation in the North Atlantic reduces the warming in this area and consequently moderates the effect on the European climate. Sea level is estimated to increase by around 15 cm because of thermal expansion of sea water; however, it appears likely that there may also be an increased accumulation of ice on Antarctica and probably Greenland which may at least partly compensate for this increase. Possible changes in the vegetation following a climate change have been estimated by evaluating the response of a biome model. This shows minor changes in the vegetation; over Europe and North America a small north-eastward movement of the vegetation zones.