Abstract: Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

Abstract: Aerosols counteract part of the warming effects of greenhouse gases, mostly by increasing the amount of sunlight reflected back to space. However, the ways in which aerosols affect climate through their interaction with clouds are complex and incompletely captured by climate models. As a result, the radiative forcing (that is, the perturbation to Earth's energy budget) caused by human activities is highly uncertain, making it difficult to predict the extent of global warming ( 1 , 2 ). Recent advances have led to a more detailed understanding of aerosol-cloud interactions and their effects on climate, but further progress is hampered by limited observational capabilities and coarse-resolution climate models.

Abstract: A global warming of 2 C relative to pre-industrial climate has been considered as a threshold which society should endeavor to remain below, in order to limit the dangerous effects of anthropogenic climate change. The possible changes in regional climate under this target level of global warming have so far not been investigated in detail. Using an ensemble of 15 regional climate simulations downscaling six transient global climate simulations, we identify the respective time periods corresponding to 2 C global warming, describe the range of projected changes for the European climate for this level of global warming, and investigate the uncertainty across the multi-model ensemble. Robust changes in mean and extreme temperature, precipitation, winds and surface energy budgets are found based on the ensemble of simulations. The results indicate that most of Europe will experience higher warming than the global average. They also reveal strong distributional patterns across Europe, which will be important in subsequent impact assessments and adaptation responses in different countries and regions. For instance, a North‐South (West‐East) warming gradient is found for summer (winter) along with a general increase in heavy precipitation and summer extreme temperatures. Tying the ensemble analysis to time periods with a prescribed global temperature change rather than fixed time periods allows for the identification of more robust regional patterns of temperature changes due to removal of some of the uncertainty related to the global models’ climate sensitivity.

Abstract: Understanding climate sensitivity is critical to projecting climate change in response to a given forcing scenario. Recent analyses have suggested that transient climate sensitivity is at the low end of the present model range taking into account the reduced warming rates during the past 10-15 years during which forcing has increased markedly. In contrast, comparisons of modelled feedback processes with observations indicate that the most realistic models have higher sensitivities. Here I analyse results from recent climate modelling intercomparison projects to demonstrate that transient climate sensitivity to historical aerosols and ozone is substantially greater than the transient climate sensitivity to CO2. This enhanced sensitivity is primarily caused by more of the forcing being located at Northern Hemisphere middle to high latitudes where it triggers more rapid land responses and stronger feedbacks. I find that accounting for this enhancement largely reconciles the two sets of results, and I conclude that the lowest end of the range of transient climate response to CO2 in present models and assessments (less than 1.3 C) is very unlikely.

Abstract: , 1444 (2008); 320 Science Gordon B. Bonan Benefits of Forests Forests and Climate Change: Forcings, Feedbacks, and the Climate This copy is for your personal, non-commercial use only. clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles ): November 5, 2014 www.sciencemag.org (this information is current as of The following resources related to this article are available online at http://www.sciencemag.org/content/320/5882/1444.full.html version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/content/suppl/2008/06/12/320.5882.1444.DC1.html can be found at: Supporting Online Material http://www.sciencemag.org/content/320/5882/1444.full.html#related found at: can be related to this article A list of selected additional articles on the Science Web sites http://www.sciencemag.org/content/320/5882/1444.full.html#ref-list-1 , 14 of which can be accessed free: cites 45 articles This article 103 article(s) on the ISI Web of Science cited by This article has been http://www.sciencemag.org/content/320/5882/1444.full.html#related-urls 74 articles hosted by HighWire Press; see: cited by This article has been http://www.sciencemag.org/cgi/collection/atmos Atmospheric Science subject collections: This article appears in the following

Abstract: Data from the Coupled Model Intercomparison Project Phase 5 for historical and future climate scenarios are examined for changes in the energy cycle component of land surface feedback on the atmosphere, namely, through the linkages from soil moisture to sensible heat flux to the height of the lifting condensation level marking the cloud base. Climate models project heightened sensitivity in both of these segments of the feedback pathway over most of the globe. This is in agreement with studies showing similar increases in land-atmosphere feedback through the water cycle, despite different physical processes, and may contribute to prevalent droughts and floods found in most climate change forecasts.

Abstract: The surface of the Earth is a three-dimensional system that is dominated by water that can exist in three phases: solid, liquid, and vapor. At any point in the evolution of the Earth’s climate, randomly varying factors such as winds, ocean currents, air masses, cloud formation, volcanic eruption, the spinning of the Earth, and other factors produce daily, monthly, and yearly fluctuations in the weather in various regions. If we average out these fluctuations over the whole Earth over a period of time, we can attempt to attribute a climate to the Earth over that time period. There is no universally accepted procedure for doing this.

Abstract: A variable-resolution atmospheric general circulation model (AGCM) is used for climate change projections over the Antarctic. The present-day simulation uses prescribed observed sea surface conditions, while a set of five simulations for the end of the twenty-first century (2070–99) under the Special Report on Emissions Scenarios (SRES) A1B scenario uses sea surface condition anomalies from selected coupled ocean–atmosphere climate models from phase 3 of the Coupled Model Intercomparison Project (CMIP3). Analysis of the results shows that the prescribed sea surface condition anomalies have a very strong influence on the simulated climate change on the Antarctic continent, largely dominating the direct effect of the prescribed greenhouse gas concentration changes in the AGCM simulations. Complementary simulations with idealized forcings confirm these results. An analysis of circulation changes using self-organizing maps shows that the simulated climate change on regional scales is not principally c...

Abstract: Coupled climate model simulations of volcanic eruptions and abrupt changes in CO2 concentration are compared in multiple realizations of the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (GFDL CM2.1). The change in global-mean surface temperature (GMST) is analyzed to determine whether a fast component of the climate sensitivity of relevance to the transient climate response (TCR; defined with the 1% yr−1 CO2-increase scenario) can be estimated from shorter-time-scale climate changes. The fast component of the climate sensitivity estimated from the response of the climate model to volcanic forcing is similar to that of the simulations forced by abrupt CO2 changes but is 5%–15% smaller than the TCR. In addition, the partition between the top-of-atmosphere radiative restoring and ocean heat uptake is similar across radiative forcing agents. The possible asymmetry between warming and cooling climate perturbations, which may affect the utility of volcanic eruptions for estimating th...

Abstract: A high resolution regional climate model (RCM) is used to simulate climate of the recent past and to project future climate change across the northeastern US. Different types of uncertainties in climate simulations are examined by driving the RCM with different boundary data, applying different emissions scenarios, and running an ensemble of simulations with different initial conditions. Empirical orthogonal functions analysis and K-means clustering analysis are applied to divide the northeastern US region into four climatologically different zones based on the surface air temperature (SAT) and precipitation variability. The RCM simulations tend to overestimate SAT, especially over the northern part of the domain in winter and over the western part in summer. Statistically significant increases in seasonal SAT under both higher and lower emissions scenarios over the whole RCM domain suggest the robustness of future warming. Most parts of the northeastern US region will experience increasing winter precipitation and decreasing summer precipitation, though the changes are not statistically significant. The greater magnitude of the projected temperature increase by the end of the twenty-first century under the higher emissions scenario emphasizes the essential role of emissions choices in determining the potential future climate change.

Abstract: Over the last 20 years, developments in climatology have provided an amazing array of explanations for the pattern of world climates. This textbook examines the Earth’s climate systems in light of this incredible growth in data availability, data retrieval systems, and satellite and computer applications. It considers regional climate anomalies, developments in teleconnections, unusual sequences of recent climate change, and human impacts on the climate system. The physical climate forms the main part of the book, but social and economic aspects of the global climate system are also considered. This textbook has been derived from the authors’ extensive experience of teaching climatology and atmospheric science. Each chapter contains an essay by a specialist in the field to enhance the understanding of selected topics. An extensive bibliography and lists of websites are included for further study. This textbook will be invaluable to advanced students of climatology and atmospheric science.

Abstract: This study assesses how climate impacts on agriculture may change the evolution of the agricultural and energy systems in meeting the end-of-century radiative forcing targets of the representative concentration pathways (RCPs). We build on the recently completed Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) exercise that has produced global gridded estimates of future crop yields for major agricultural crops using climate model projections of the RCPs from the Coupled Model Intercomparison Project Phase 5 (CMIP5). For this study we use the bias-corrected outputs of the HadGEM2-ES climate model as inputs to the LPJmL crop growth model, and the outputs of LPJmL to modify inputs to the GCAM integrated assessment model. Our results indicate that agricultural climate impacts generally lead to an increase in global cropland, as compared with corresponding emissions scenarios that do not consider climate impacts on agricultural productivity. This is driven mostly by negative impacts on wheat, rice, other grains, and oil crops. Still, including agricultural climate impacts does not significantly increase the costs or change the technological strategies of global, whole-system emissions mitigation. In fact, to meet the most aggressive climate change mitigation target (2.6 W/m2 in 2100), the net mitigation costs are slightly lower when agricultural climate impacts are considered. Key contributing factors to these results are (a) low levels of climate change in the low-forcing scenarios, (b) adaptation to climate impacts simulated in GCAM through inter-regional shifting in the production of agricultural goods, and (c) positive average climate impacts on bioenergy crop yields.

Abstract: The comprehensive general circulation model ECHAM6 is used in a radiative-convective equilibrium configuration. It is coupled to a perfectly conducting slab. To understand the local impact of thermodynamic surface properties on the land-ocean warming contrast, the surface latent heat flux and surface heat capacity are reduced stepwise, aiming for a land-like climate. Both ocean-like and land-like RCE simulation reproduce the tropical atmosphere over ocean and land in a satisfactory manner and lead to reasonable land-ocean warming ratios. A small surface heat capacity induces a high diurnal surface temperature range which triggers precipitation during the day and decouples the free troposphere from the diurnal mean temperature. With increasing evaporation resistance, the net atmospheric cooling rate decreases because cloud base height rises, causing a reduction of precipitation. Climate sensitivity depends more on changes in evaporation resistance than on changes in surface heat capacity. A feedback analysis with the partial radiation perturbation method shows that amplified warming over idealized land can be associated with disproportional changes in the lapse rate versus the water vapor feedback. Cloud feedbacks, convective aggregation, and changes in global mean surface temperature confuse the picture.

Abstract: Motivated by proposals to compensate CO2-induced warming with a decrease in solar radiation, this study investigates how single-forcing simulations should be combined to best represent the spatial patterns of surface temperature and precipitation of idealized geoengineering scenarios. Using instantaneous and transient simulations with changing CO2 and solar forcings, we show that a geoengineering scenario, i.e., a scenario where the solar constant is reduced as CO2 concentrations are increased, is better represented by subtracting the response pattern of a solar forcing increase simulation from the response pattern of a CO2 forcing increase simulation, than by adding the response pattern of a solar forcing decrease simulation to a CO2 forcing increase simulation. The reason is a asymmetric response of the climate system to a forcing increase or decrease between both hemispheres. In particular, the Atlantic meridional overturning circulation responds faster to a solar forcing decrease compared to a solar forcing increase. Further, the climate feedbacks are state and region dependent, which is particularly apparent in the polar regions due to the sea ice-albedo feedback. The importance of understanding the local response of the climate system to geoengineering and single-forcing scenarios is highlighted, since these aspects are hardly discernible when only global mean values are considered.

Abstract: Projections of future climate change by climate system models depend on the sensitivities of models to specified greenhouse gases. To reveal and understand the different climate sensitivities of two versions of LASG/IAP climate system model FGOALS-g2 and FGOALS-s2, we investigate the global mean surface air temperature responses to idealized CO2 forcing by using the output of abruptly quadrupling CO2 experiments. The Gregory-style regression method is used to estimate the “radiative forcing” of quadrupled CO2 and equilibrium sensitivity. The model response is separated into a fast-response stage associated with the CO2 forcing during the first 20 years, and a slow-response stage post the first 20 years. The results show that the radiative forcing of CO2 is overestimated due to the positive water-vapor feedback and underestimated due to the fast cloud processes. The rapid response of water vapor in FGOALS-s2 is responsible for the stronger radiative forcing of CO2. The climate sensitivity, defined as the equilibrium temperature change under doubled CO2 forcing, is about 3.7 K in FGOALS-g2 and 4.5 K in FGOALS-s2. The larger sensitivity of FGOALS-s2 is due mainly to the weaker negative longwave clear-sky feedback and stronger positive shortwave clear-sky feedback at the fast-response stage, because of the more rapid response of water vapor increase and sea-ice decrease in FGOALS-s2 than in FGOALS-g2. At the slow-response stage, similar to the fast-response stage, net negative clear-sky feedback is weaker in FGOALS-s2. Nevertheless, the total negative feedback is larger in FGOALS-s2 due to a larger negative shortwave cloud feedback that involves a larger response of total cloud fraction and condensed water path increase. The uncertainties of estimated forcing and net feedback mainly come from the shortwave cloud processes.

Abstract: Climate change, arising from the greenhouse effect of heattrapping gases, is a global problem. All nations are involved in both its causes and consequences. Currently developed nations are the largest emitters of greenhouse gases, but emissions by developing nations will grow considerably in coming decades. The most recent scientific evidence indicates that effects during the twenty-first century may range from a global temperature increase of 1.1oC (2oF) up to 6.4oC. In addition to simply warming the planet, other predicted effects include extreme weather phenomena such as floods, droughts, tornadoes, increased shoreline erosion seas and oceans.

Abstract: This Chapter proposes a framework for understanding the implications of climate change for the oceans; the conclusions its reaches center around the various ways in which humanity interacts with the oceans. The role of law in efforts to mitigate the greenhouse gas emissions from shipping and offshore oil exploration is apparent; however, the law is less clear or developed in terms of possible geo-engineering initiatives focusing on the oceans. The role of law in mitigation efforts has been subject to some scholarly assessment; but the scholarly agenda regarding the role of law in the challenges presented by adaptation to movements in fish, the rise in sea level and the loss of marine life due to increased acidity is not clear. The scope of these latter challenges is truly global and foundational yet present scholarly work tends only to nibble at the edges of these issues. These challenges will require creativity in the academy, and in international relations will demand substantial cooperative international frameworks so that.conflict and suffering may be minimised. What are the impacts of climate change for the ocean? Name any physical characteristic of the oceans, and it will change. Three fundamental impacts of increased carbon dioxide focused upon in this Chapter are: (1) an increase in water temperature, (2) a rise in sea level, and (3) an increase in the ocean's acidity level. Following the approach of the Intergovernmental Panel on Climate Change ("IPCC"), the Chapter first considers ocean-based strategies to mitigate change in the climate by reducing the levels of climate-changing gases in the atmosphere; and, second, considers the challenges posed by the need to adapt to the likely impacts of climate change.

Abstract: The response of sea ice to climate change affects Earth’s radiative properties in ways that contribute to yet more climate change. Here, a configuration of the Community Earth System Model, version 1.0.4 (CESM 1.0.4), with a slab ocean model and a thermodynamic–dynamic sea ice model is used to investigate the overall contribution to climate sensitivity of feedbacks associated with the sea ice loss. In simulations in which sea ice is not present and ocean temperatures are allowed to fall below freezing, the climate feedback parameter averages ~1.31 W m−2 K−1; the value obtained for control simulations with active sea ice is ~1.05 W m−2 K−1, indicating that, in this configuration of CESM1.0.4, sea ice response accounts for ~20% of climate sensitivity to an imposed change in radiative forcing. In this model, the effect of sea ice response on the longwave climate feedback parameter is nearly half as important as its effect on the shortwave climate feedback parameter. Further, it is shown that the stre...

Abstract: Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Abstract: 1. Climate Change in the Public Sphere 1.1. Communicating about climate change 1.2. The state of the science 1.3. Responding to climate change: mitigation and adaptation 1.4. The state of the policy 1.4.1. The United Nations Framework Convention on Climate Change and the Kyoto Protocol 1.4.2. The United Nations Conference on Environment and Development (Rio, and Rio +20) 1.4.3. The Intergovernmental Panel on Climate Change 1.5. The scale of the challenge: accelerating action on climate change 1.6. Roadmap to the book 2. Basic System Dynamics 2.1. What's a system? 2.1.1. System parts and interactions 2.1.2. Stocks and flows 2.1.3. Feedbacks 2.1.4. Lags 2.1.5. Function or purpose 2.2. Earth's Climate System: The parts and interconnections 2.2.1. Atmosphere, Hydrosphere, Biosphere, Geosphere, and Anthroposphere 2.2.2. The Ins and Out of Earth's Energy Budget 3. Climate controls: Energy from the Sun 3.1. Incoming Solar Radiation 3.1.1. Blackbody radiation: the Sun versus Earth 3.1.2. Our place in space: the Goldilocks planet 3.2. Natural Variability 3.2.1. 4.5 billion years of solar energy 3.2.2. Orbital controls: baseline variability in the past million years 3.2.3. Sunspots: how big a deal? 3.3. Mitigation strategies and policy tools 4. Climate Controls: Earth's Reflectivity 4.1. Natural Variability 4.1.1. At Earth's surface: Ice, water, and vegetation 4.1.2. In the atmosphere: Aerosols and clouds 4.2. Anthropogenic Variability 4.2.1. Land-use changes 4.2.2. Anthropogenic Aerosols 4.3. Mitigation strategies and policy tools 5. Climate Controls: The Greenhouse effect 5.1. How does the greenhouse effect work? 5.1.1. Characteristics of a good greenhouse gas 5.1.2. Energy flows in a greenhouse world 5.2. The unperturbed carbon cycle and natural greenhouse variability 5.2.1. Carbon stocks and flows 5.2.2. Timescales of natural greenhouse variability 5.2.3. Feedbacks involving the greenhouse effect 5.3. Anthropogenic interference 5.3.1. Perturbed stocks, flows, and chemical fingerprints 5.3.2. Cumulative carbon emissions: a budget 6. The Core of Climate Change Mitigation: Reducing Greenhouse Gas Emissions and Transforming the Energy System 6.1. Introduction to reducing greenhouse gas emissions 6.2. The Global Energy System 6.3. Mitigation Strategies 6.3.1. Demand-side mitigation: energy efficiency and conservation 6.3.2. Supply-side mitigation 6.3.3. Carbon capture and storage 6.4. Fostering accelerated and transformative mitigation 7. Climate Models 7.1. Climate Model Basics 7.1.1. Physical Principles 7.1.2. The Role of Observations 7.1.3. Time and Space 7.1.4. Parameterization 7.1.5. Testing climate models 7.2. Types of climate models 7.2.1. Energy Balance Models 7.2.2. Earth System Models of Intermediate Complexity 7.2.3. General Circulation Models 7.2.4. Regional Climate Models 7.2.5. Integrated Assessment Models 7.3. Certainties and Uncertainties 8. Future Climate: Emissions, climate, and what we do about it 8.1. Emissions scenarios SRES scenario 'families' and storylines 8.1.1. Post-SRES and Representative Concentration Pathways 8.1.2. 8.2. Global Climate in 2100 Temperature, precipitation, sea level rise, and extreme events 8.2.1. Uncertainty 8.2.2. 8.3. Regional forecasting 8.4. Backcasting 8.5. Scale of the challenge: Transforming emissions pathways 9. Climate Change Impacts on Natural Systems 9.1. Observed Impacts Impacts on Land 9.1.1. Impacts in the Oceans 9.1.2. 9.2. Adaptation in Natural Systems 9.3. Policy Tools and Progress International tools 9.3.1. National and sub-national tools 9.3.2. 9.4. Conclusions 10. Climate Change Impacts on Human Systems 10.1. Introduction 10.2. Key concepts in climate change impacts and adaptation 10.3. Observed and Projected Impacts 10.3.1. Climate change impacts on food and water 10.3.2. Climate change impacts on cities and infrastructure 10.3.3. Equity implications: Health, culture, and global distribution of wealth 10.4. Adaptation in human systems 10.5. Policy Tools and Progress 10.5.1. Policy tools for adaptation 10.5.2. International and national adaptation 10.5.3. Sub-national adaptation 10.5.4. Social movements and human behavior change: the root of the adaptation conundrum 11. The Frontier: Innovative Action on Climate Change 11.1. Integrating Adaptation and Mitigation: Pursuing Sustainability 11.2. What Road will we choose? The ethics of geoengineering 11.3. Transformative change: reorienting development paths to yield a sustainable future 11.4. Conclusions and future directions

Abstract: An evaluation of atmospheric convective mixing and low-level clouds in climate models suggests that Earth's climate will warm more than was thought in response to increasing levels of carbon dioxide. See Article p.37

Abstract: The subject area Climate Change includes information relating to the effect of energy use on the Earth’s climate. The earliest step in this respect was the basic realization that climate can change. This required first, accurate methods of measuring temperature, rainfall, and other weather conditions and events, and second, the ability to track these conditions and events over an extended time to identify changing climate patterns.

Abstract: According to this study the commonly applied radiative forcing (RF) value of 3.7 Wm-2 for CO2 concentration of 560 ppm includes water feedback. The same value without water feedback is 2.16 Wm -2 which is 41.6 % smaller. Spectral analyses show that the contribution of CO2 in the greenhouse (GH) phenomenon is about 11 % and water’s strength in the present climate in comparison to CO2 is 15.2. The author has analyzed the value of the climate sensitivity (CS) and the climate sensitivity parameter () using three different calculation bases. These methods include energy balance calculations, infrared radiation absorption in the atmosphere, and the changes in outgoing longwave radiation at the top of the atmosphere. According to the analyzed results, the equilibrium CS (ECS) is at maximum 0.6 °C and the best estimate of  is 0.268 K/(Wm-2) without any feedback mechanisms. The latest warming scenarios of Intergovernmental Panel on Climate Change (IPCC) for different CO2 concentrations until the year 2100 include the same feedbacks as the 2011 warming i.e. only water feedback. The ECS value of 3.0 °C would mean that other feedback mechanisms should be stronger than water feedback. So far there is no evidence about these mechanisms, even though 40 % of the change from 280 ppm to 560 ppm has already happened. The relative humidity trends since 1948 show descending development which gives no basis for using positive water feedback in any warming calculations. Cloudiness changes could explain the recent stagnation in global warming.

Abstract: The IPCC 5th Assessment Report (Climate Change 2013: The Physical Science Basis) was accepted at the 36th Session of the IPCC on 26 September 2013 in Stockholm, Sweden. It consists of the full scientific and technical assessment undertaken by Working Group I. This comprehensive assessment of the physical aspects of climate change puts a focus on those elements that are relevant to understand past, document current, and project future of climate change. The assessment builds on the IPCC Fourth Assessment Report and the recent Special Report on Managing the Risk of Extreme Events and Disasters to Advance Climate Change Adaptation. The assessment covers the current knowledge of various processes within, and interactions among, climate system components, which determine the sensitivity and response of the system to changes in forcing, and they quantify the link between the changes in atmospheric constituents, and hence radiative forcing, and the consequent detection and attribution of climate change. Projections of changes in all climate system components are based on model simulations forced by a new set of scenarios. The report also provides a comprehensive assessment of past and future sea level change in a dedicated chapter. The primary purpose of this Technical Summary is to provide the link between the complete assessment of the multiple lines of independent evidence presented in the main report and the highly condensed summary prepared as Policy makers Summary. The Technical Summary thus serves as a starting point for those readers who seek the full information on more specific topics covered by this assessment. Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased. Total radiative forcing is positive, and has led to an uptake of energy by the climate system. The largest contribution to total radiative forcing is caused by the increase in the atmospheric concentration of CO₂ since 1750. Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system. Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions. The in-depth review for past, present and future of climate change is carried out on the basis of the IPCC 5th Assessment Report.

Abstract: The Intergovernmental Panel on Climate Change (IPCC) recently published a Supplementary Report updating and supporting the First Assessment of 1990 and their findings are summarised here. If greenhouse emissions continue at the present level, the Report estimates a global temperature increase of 0.3% per decade – a rate probably greater than any since the last ice age. Sulphur pollution and ozone depletion provide two complications for the assessment of global warming as they can both lead to cooling. However, neither effect should have much influence on the long–term problem of warming.

Abstract: The recent work by Shindell usefully contributes to the debate over estimating climate sensitivity by highlighting an important aspect of the climate system: that climate forcings that occur over land result in a more rapid temperature response than forcings that are distributed more uniformly over the globe. While, as noted in this work, simple climate models may be biased by assuming the same temperature response for all forcing agents, the implication that the MAGICC model is biased in this way is not correct.