Abstract: Integrated assessment models estimate the impact of climate change on current economic output, but not on its rate of growth. This study modifies a standard integrated assessment model to allow climate change to directly affect gross GDP growth rates. Results show that climate change significantly slows down GDP growth in poor regions but not in rich countries, with implications for the level of near-term mitigation.

Abstract: Experiments with CO2 instantaneously quadrupled and then held constant are used to show that the relationship between the global-mean net heat input to the climate system and the global-mean surface air temperature change is nonlinear in phase 5 of the Coupled Model Intercomparison Project (CMIP5) atmosphere–ocean general circulation models (AOGCMs). The nonlinearity is shown to arise from a change in strength of climate feedbacks driven by an evolving pattern of surface warming. In 23 out of the 27 AOGCMs examined, the climate feedback parameter becomes significantly (95% confidence) less negative (i.e., the effective climate sensitivity increases) as time passes. Cloud feedback parameters show the largest changes. In the AOGCM mean, approximately 60% of the change in feedback parameter comes from the tropics (30°N–30°S). An important region involved is the tropical Pacific, where the surface warming intensifies in the east after a few decades. The dependence of climate feedbacks on an evolving p...

Abstract: Presents information, charts and graphs showing measured climate changes across 40 indicators related to greenhouse gases, weather and climate, oceans, snow and ice, heath and society, and ecosystems.

Abstract: We designed scenarios for impact assessment that explicitly address policy choices and uncertainty in climate response. Economic projections and the resulting greenhouse gas emissions for the “no climate policy” scenario and two stabilization scenarios: at 4.5 W/m2 and 3.7 W/m2 by 2100 are provided. They can be used for a broader climate impact assessment for the US and other regions, with the goal of making it possible to provide a more consistent picture of climate impacts, and how those impacts depend on uncertainty in climate system response and policy choices. The long-term risks, beyond 2050, of climate change can be strongly influenced by policy choices. In the nearer term, the climate we will observe is hard to influence with policy, and what we actually see will be strongly influenced by natural variability and the earth system response to existing greenhouse gases. In the end, the nature of the system is that a strong effect of policy, especially directed toward long-lived GHGs, will lag by 30 to 40 years its implementation.

Abstract: The results of an ensemble of regional climate model (RCM) simulations over South America are presented. This is the first coordinated exercise of regional climate modelling studies over the continent, as part of the CLARIS-LPB EU FP7 project. The results of different future periods, with the main focus on (2071–2100) is shown, when forced by several global climate models, all using the A1B greenhouse gases emissions scenario. The analysis is focused on the mean climate conditions for both temperature and precipitation. The common climate change signals show an overall increase of temperature for all the seasons and regions, generally larger for the austral winter season. Future climate shows a precipitation decrease over the tropical region, and an increase over the subtropical areas. These climate change signals arise independently of the driving global model and the RCM. The internal variability of the driving global models introduces a very small level of uncertainty, compared with that due to the choice of the driving model and the RCM. Moreover, the level of uncertainty is larger for longer horizon projections for both temperature and precipitation. The uncertainty in the temperature changes is larger for the subtropical than for the tropical ones. The current analysis allows identification of the common climate change signals and their associated uncertainties for several subregions within the South American continent.

Abstract: Surface waves in the ocean respond to variability and changes of climate. Observations and modeling studies indicate trends in wave height over the past decades. Nevertheless, it is currently impossible to discern whether these trends are the result of climate variability or change. The output of an Earth system model (EC-EARTH) produced within phase 5 of the Coupled Model Intercomparison Project (CMIP5) is used here to force a global Wave Model (WAM) in order to study the response of waves to different climate regimes. A control simulation was run to determine the natural (unforced) model variability. A simplified fingerprint approach was used to calculate positive and negative limits of natural variability for wind speed and significant wave height, which were then compared to different (forced) climate regimes over the historical period (1850–2010) and in the future climate change scenario RCP8.5 (2010–2100). Detectable climate change signals were found in the current decade (2010–20) in the No...

Abstract: Research on Quaternary climate change is reviewed from the perspective of the real or potential contribution to improving our ability to predict the climate of the future. For convenience the literature is divided into four timescales: orbital, sub-Milankovitch, Holocene and the last 2000 years. Four ‘challenges’ provide a framework for discussion: better understanding of the way the climate system works, better forecasting of the drivers of climate change, improved estimates of climate sensitivity (change in global mean annual temperature per unit increase in forcing) and evaluation of the models used to predict the climate of the future. Although a great deal of progress has been made, it is concluded that there are some aspects of our scientific culture that limit our potential. These include our tradition of storytelling rather than critical hypothesis testing, an over-emphasis on the role of surface water sinking in the far north Atlantic as a driver of ocean circulation and an attendant under-emphasis on the critical importance of changes in atmospheric circulation, and a lack of rigour in testing the hypothesis that changes in solar irradiance are an important driver of climate change.

Abstract: The paper presents a model-based approach describing the impacts of climate change on the European energy system. Existing analyses only estimate a limited range of climate impacts over a limited geographical area. Using the POLES model and the results from several climate models, the present paper quantifies the main impacts of climate change on the European energy sector, country by country, thus achieving progress in this direction. As far as energy demand is concerned, our main finding is that higher temperatures will mean that air-conditioning will consume more energy, reaching about 53 Mtoe by 2100 in a scenario with no strong emissions constraints (A1B). On the other hand, less energy will be consumed for heating buildings, falling by about 65 Mtoe per year. This represents a net decrease in energy consumption of about 12 Mtoe by 2100. On the supply side, more constrained and expensive operating conditions for electric power plants will result in lower electricity generation by thermal, nuclear and hydro-power plants, with a maximum decrease of about 200 TWh in 2070 in the A1B scenario and 150 TWh in 2060 and 2080 for a low emissions scenario (E1). These effects vary a great deal across Europe and remain very dependent on the uncertainties affecting the results of the various climate models. This overall uncertainty may inhibit effective decisions. However, the study offers insights not otherwise available without the full coverage of the energy system provided by POLES and climate features provided by climate models. The study identifies the main impacts of climate change in a strategic sector and provides an “order of magnitude” or “central trend” for these impacts, which might be useful in an adaptive policy of act, learn and then act again.

Abstract: The ocean stores more than 90% of the energy excess associated with anthropogenic climate change. The resulting ocean warming and thermal expansion are leading contributors to global mean sea level (GMSL) rise. Confidence in projections of GMSL rise therefore depends on the ability of climate models to reproduce global mean thermosteric sea level (GMTSL) rise over the twentieth century. This study first compares the GMTSL of the climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to observations over 1961–2005. Although the model ensemble mean is within the uncertainty of observations, the model ensemble exhibits a large spread. The authors then aim to explain the spread in CMIP5 climate model GMTSL over the twentieth and twenty-first centuries. It is shown that the climate models’ GMTSL rise depends linearly on the time-integrated radiative forcing F (under continuously increasing radiative forcing). The constant of proportionality μ expresses the transient thermoster...

Abstract: We use both prescribed sea surface temperature and fully coupled versions of the Geophysical Fluid Dynamics Laboratory coupled climate model (CM3) to analyze the sensitivity of radiative forcing, ocean heat uptake, and climate feedback to changes in anthropogenic greenhouse gases and aerosols considered separately over the 1870 to 2005 period. The global anthropogenic aerosol climate feedback parameter (− α) of −1.13 ± 0.33 Wm−2 K−1 is indistinguishable from the greenhouse gas − α of −1.28 ± 0.23 Wm−2 K−1. However, this greenhouse gas climate feedback parameter is about 50% larger than that obtained for CM3 from a widely used linear extrapolation method of regressing Earth's top of atmosphere imbalance against surface air temperature change in idealized CO2 radiative forcing experiments. This implies that the global mean surface temperature change due to forcing over the 1870–2005 period is 50% smaller than that predicted using the climate feedback parameter obtained from idealized experiments. This difference results from time dependence in α, which makes the radiative forcing obtained by the fixed sea surface temperature method incompatible with that obtained by the linear extrapolation method fitted over the first 150 years after CO2 is quadrupled. On a regional scale, α varies greatly between the greenhouse gas and aerosol case. This suggests that the relationship between transient and equilibrium climate sensitivities obtained from idealized CO2 simulations, using techniques such as regional feedback analysis and heat uptake efficacy, may not hold for other forcing scenarios.

Abstract: The present day global climate change is fueled by our use of fossil fuels and land use change. The already observed warming and other distinct changes in the climate system stem from these human influences and are ongoing. Due to climate system inertia, a part of the climate system's response to this historical forcing remains to manifest itself, which it will do over time. At the same time, socio-economic forces and trends imply some amount of additional emission and land use change, which compounds our commitment to even more substantial climate change. Cumulative carbon dioxide emissions are the basic determinant of the ultimate amount of anthropogenic climate change. Climate system properties, such as climate sensitivity and the carbon cycle, and also possible initiation of non-linear changes, further shape the amount and nature of the long-term change for any set amount of greenhouse gas emissions. While a changed climate is, in practice, now unavoidable, our commitment to continued climate change can be constrained by reductions of global carbon dioxide emissions, their cessation and/or negative emissions. These alternatives have different implications for the long-term unfolding of these changes, but can all considerably reduce the possibility of very large amounts of change, the need for adaptation and responses to negative impacts. (Less)

Abstract: Changes in Earth’s climate are influenced by internal climate variability and external forcings, such as changes in solar radiation, volcanic eruptions, anthropogenic greenhouse gases (GHG), and aerosols. Although the response of surface temperature to external forcings has been studied extensively, this has not been done for sea level. Here, a range of climate model experiments for the twentieth century is used to study the response of global and regional sea level change to external climate forcings. Both the global mean thermosteric sea level and the regional dynamic sea level patterns show clear responses to anthropogenic forcings that are significantly different from internal climate variability and larger than the difference between models driven by the same external forcing. The regional sea level patterns are directly related to changes in surface winds in response to the external forcings. The spread between different realizations of the same model experiment is consistent with internal c...

Abstract: The paper presents a model-based approach describing the impacts of climate change on the European energy system. Existing analyses only estimate a limited range of climate impacts over a limited geographical area. Using the POLES model and the results from several climate models, the present paper quantifies the main impacts of climate change on the European energy sector, country by country, thus achieving progress in this direction. As far as energy demand is concerned, our main finding is that higher temperatures will mean that air-conditioning will consume more energy, reaching about 53 Mtoe by 2100 in a scenario with no strong emissions constraints (A1B). On the other hand less energy will be consumed for heating buildings, falling by about 65 Mtoe per year. This represents a net decrease in energy consumption of about 12 Mtoe by 2100. On the supply side, more constrained and expensive operating conditions for electric power plants will result in lower electricity generation by thermal, nuclear and hydro-power plants, with a maximum decrease of about 200 TWh in 2070 in the A1B scenario and 150 TWh in 2060 and 2080 for a low emissions scenario (E1). These effects vary a great deal across Europe and remain very dependent on the uncertainties affecting the results of the various climate models. This overall uncertainty may inhibit effective decisions. However the study offers insights not otherwise available without the full coverage of the energy system provided by POLES and climate features provided by climate models. The study identifies the main impacts of climate change in a strategic sector and provides an "order of magnitude" or "central trend" for these impacts, which might be useful in an adaptive policy of act, learn and then act again.

Abstract: An attempt to reconcile the effects of temperature on economic productivity at the micro and macro levels produces predictions of global economic losses due to climate change that are much higher than previous estimates. See Letter p.235 Temperature, and therefore climate change, can affect a country's economic productivity, but it has not been clear if rich and poor countries, or different aspects of economic productivity, show similar relationships. These authors use economic data from 166 countries for the years 1960 to 2010 to uncover a universal nonlinear relationship that reconciles earlier results. Economic productivity peaks at an annual average temperature of 13 °C, and the authors explore the likelihood of global economic contraction under future warming scenarios.

Abstract: Sea-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

Abstract: Projected climate change integrates the net response to multiple climate feedbacks. Whereas existing long-term climate change projections are typically based on unweighted individual climate model simulations, as observed climate change intensifies it is increasingly becoming possible to constrain the net response to feedbacks and hence projected warming directly from observed climate change. One approach scales simulated future warming based on a fit to observations over the historical period, but this approach is only accurate for near-term projections and for scenarios of continuously increasing radiative forcing. For this reason, the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) included such observationally constrained projections in its assessment of warming to 2035, but used raw model projections of longer term warming to 2100. Here a simple approach to weighting model projections based on an observational constraint is proposed which does not assume a linear relationship between past and future changes. This approach is used to weight model projections of warming in 2081–2100 relative to 1986–2005 under the Representative Concentration Pathway 4.5 forcing scenario, based on an observationally constrained estimate of the Transient Climate Response derived from a detection and attribution analysis. The resulting observationally constrained 5–95% warming range of 0.8–2.5 K is somewhat lower than the unweighted range of 1.1–2.6 K reported in the IPCC AR5.

Abstract: Regional climate models (RCMs) are important tools used for downscaling climate simulations from global scale models. In project CECILIA, two RCMs were used to provide climate change information for regions of Central and Eastern Europe. Models RegCM and ALADIN-Climate were employed in downscaling global simulations from ECHAM5 and ARPEGE-CLIMAT under IPCC A1B emission scenario in periods 2021–2050 and 2071–2100. Climate change signal present in these simulations is consistent with respective driving data, showing similar large-scale features: warming between 0 and 3°C in the first period and 2 and 5°C in the second period with the least warming in northwestern part of the domain increasing in the southeastern direction and small precipitation changes within range of

Abstract: The wind climate and its possible change in a warming world are important topics for many applications, among which are marine and coastal safety and wind energy generation. Therefore, wind is an important variable to investigate for climate change scenarios. In developing the wind part of the KNMI'14 climate change scenarios, output from several model categories have been analysed, ranging from global General Circulation Models via regional climate model (RCMs) to suitably re-sampled RCM output. The main conclusion is that global warming will not change the wind climate over the Netherlands and the North Sea beyond the large range of natural climate variability that has been experienced in the past.

Abstract: We present a meta-regression analysis of the relation between the concentration of carbon dioxide in the atmosphere and changes in global temperature. The relation is captured by “climate sensitivity,” which measures the response to a doubling of carbon dioxide concentrations compared to pre-industrial levels. Estimates of climate sensitivity play a crucial role in evaluating the impacts of climate change and constitute one of the most important inputs into the computation of the social cost of carbon, which reflects the socially optimal value of a carbon tax. Climate sensitivity has been estimated by many researchers, but their results vary significantly. We collect 48 estimates from 16 studies and analyze the literature quantitatively. We find evidence for publication selection bias: researchers tend to report preferentially large estimates of climate sensitivity. Corrected for publication bias, the bulk of the literature is consistent with climate sensitivity lying between 1.4 and 2.3°C.

Abstract: This chapter introduces the basics of the climate system and climate change. How do we know climate is changing? How are future changes simulated? What causes natural and anthropogenic climate change? These questions are answered here, forming a foundation for climate change understanding that is needed to explore biological responses.

Abstract: Monckton of Brenchley et al. (Sci Bull 60:122–135, 2015) (hereafter called M15) use a simple energy balance model to estimate climate response. They select parameters for this model based on semantic arguments, leading to different results from those obtained in physics-based studies. M15 did not validate their model against observations, but instead created synthetic test data based on subjective assumptions. We show that M15 systematically underestimate warming: since 1990, most years were warmer than their modelled upper limit. During 2000–2010, RMS error and bias are approximately 150 % and 350 % larger than for the CMIP5 median, using either the Berkeley Earth or Cowtan and Way surface temperature data. We show that this poor performance can be explained by a logical flaw in the parameter selection and that selected parameters contradict observational estimates. M15 also conclude that climate has a near-instantaneous response to forcing, implying no net energy imbalance for the Earth. This contributes to their low estimates of future warming and is falsified by Argo float measurements that show continued ocean heating and therefore a sustained energy imbalance. M15’s estimates of climate response and future global warming are not consistent with measurements and so cannot be considered credible.

Abstract: As interest in climate geoengineering and the advertent manipulation of climate increases rapidly there is a tendency to overlook that we are already constructing current and future global climate through our use of greenhouse gases (GHGs). Any decisions on forms of geoengineering, enhanced or reduced GHG use will lead to a climate response and a global climate that is inevitably to some extent anthropogenically determined. It is therefore of value to pose the question: So what sort of climate do we want? In order to examine this question we need to look at a number of key questions. First, if we wish to remove any anthropological forcing of climate how do we determine and agree on what ‘natural’ climate is and will be over the next century? Second, how are the climate goals of GHG reductions/geoengineered climates defined by their proponents, i.e. what sort of climate(s) are we aiming to achieve and how have different bodies and authors defined these climates? Consideration of these questions has wider implications for how climate change discourses may change in the near future.