Abstract: We propose a simple real-time index of global human-induced warming and assess its robustness to uncertainties in climate forcing and short-term climate fluctuations. This index provides improved scientific context for temperature stabilisation targets and has the potential to decrease the volatility of climate policy. We quantify uncertainties arising from temperature observations, climate radiative forcings, internal variability and the model response. Our index and the associated rate of human-induced warming is compatible with a range of other more sophisticated methods to estimate the human contribution to observed global temperature change.

Abstract: . The Paris Agreement of December 2015 stated a goal to pursue efforts to keep global temperatures below 1.5 °C above preindustrial levels and well below 2 °C. The IPCC was charged with assessing climate impacts at these temperature levels, but fully coupled equilibrium climate simulations do not currently exist to inform such assessments. In this study, we produce a set of scenarios using a simple model designed to achieve long-term 1.5 and 2 °C temperatures in a stable climate. These scenarios are then used to produce century-scale ensemble simulations using the Community Earth System Model, providing impact-relevant long-term climate data for stabilization pathways at 1.5 and 2 °C levels and an overshoot 1.5 °C case, which are realized (for the 21st century) in the coupled model and are freely available to the community. Here we describe the design of the simulations and a brief overview of their impact-relevant climate response. Exceedance of historical record temperature occurs with 60 % greater frequency in the 2 °C climate than in a 1.5 °C climate aggregated globally, and with twice the frequency in equatorial and arid regions. Extreme precipitation intensity is statistically significantly higher in a 2.0 °C climate than a 1.5 °C climate in some specific regions (but not all). The model exhibits large differences in the Arctic, which is ice-free with a frequency of 1 in 3 years in the 2.0 °C scenario, and 1 in 40 years in the 1.5 °C scenario. Significance of impact differences with respect to multi-model variability is not assessed.

Abstract: Forty-five years after it was first proposed, climate change has revived debates around the concept of limits to growth. This Review reflects on economic perspectives on limits to growth, and proposes a third option to reduce resistance to climate policies. Climate change has revived debates around the concept of limits to growth, 45 years after it was first proposed. Many citizens, scientists and politicians fear that stringent climate policy will harm economic growth. Some are anti-growth, whereas others believe green growth is compatible with a transition to a low-carbon economy. As the window to curb warming at 2 °C closes, this debate will intensify. This Review critically reflects on both positions, providing an overview of existing literature on the growth versus climate debate. Both positions are argued here to jeopardize environmental or social goals. A third position, labelled an 'agrowth' strategy, is proposed to depolarize the debate and reduce resistance to climate policies.

Abstract: Global warming potentials (GWPs) have become an essential element of climate policy and are built into legal structures that regulate greenhouse gas emissions. This is in spite of a well-known shortcoming: GWP hides trade-offs between short- and long-term policy objectives inside a single time scale of 100 or 20 years ( 1 ). The most common form, GWP100, focuses on the climate impact of a pulse emission over 100 years, diluting near-term effects and misleadingly implying that short-lived climate pollutants exert forcings in the long-term, long after they are removed from the atmosphere ( 2 ). Meanwhile, GWP20 ignores climate effects after 20 years. We propose that these time scales be ubiquitously reported as an inseparable pair, much like systolic-diastolic blood pressure and city-highway vehicle fuel economy, to make the climate effect of using one or the other time scale explicit. Policy-makers often treat a GWP as a value-neutral measure, but the time-scale choice is central to achieving specific objectives ( 2 – 4 ).

Abstract: We examine the impact of current and future climate on crop mixes over space in the US. We find using historical data that temperature and precipitation are among the causal factors for shits in crop production location and mixes, with some crops being more sensitive than others. In particular, we find that when temperature rises, cotton, rice, sorghum and winter wheat are more likely to be chosen. We also find that barley, sorghum, winter wheat, spring wheat and hay are more likely to be chosen as regions become drier, and corn, cotton, rice and soybeans are more likely to be selected in wetter regions. Additionally, we assess how much of the observed crop mix shifts between 1970 and 2010 were contributed to by climate change. There we find climate explains about 7-50% of the shift in latitude, 20-36% in longitude and 4-28% of that in elevation. Finally, we estimate climate change impacts on future crop mix under CMIP5 scenarios. There we find shifts in US production regions for almost all major crops with the movement north and east. The estimates describe how the farmers respond to altering climate and can be used for planning future crop allocations.

Abstract: Summary In the ongoing debate about the climate benefits of fuel switching from coal to natural gas for power generation, the metrics used to model climate impacts may be important. In this article, we evaluate the life cycle greenhouse gas emissions of coal and natural gas used in new, advanced power plants using a broad set of available climate metrics in order to test for the robustness of results. Climate metrics included in the article are global warming potential, global temperature change potential, technology warming potential, and cumulative radiative forcing. We also used the Model for the Assessment of Greenhouse-gas Induced Climate Change (MAGICC) climate-change model to validate the results. We find that all climate metrics suggest a natural gas combined cycle plant offers life cycle climate benefits over 100 years compared to a pulverized coal plant, even if the life cycle methane leakage rate for natural gas reaches 5%. Over shorter time frames (i.e., 20 years), plants using natural gas with a 4% leakage rate have similar climate impacts as those using coal, but are no worse than coal. If carbon capture and sequestration becomes available for both types of power plants, natural gas still offers climate benefits over coal as long as the life cycle methane leakage rate remains below 2%. These results are consistent across climate metrics and the MAGICC model over a 100-year time frame. Although it is not clear whether any of these metrics are better than the others, the choice of metric can inform decisions based on different societal values. For example, whereas annual temperature change reported may be a more relevant metric to evaluate the human health effects of increased heat, the cumulative temperature change may be more relevant to evaluate climate impacts, such as sea-level rise, that will result from the cumulative warming.

Abstract: Global vegetation models and terrestrial carbon cycle models are widely used for projecting the carbon balance of terrestrial ecosystems. Ensembles of such models show a large spread in carbon balance predictions, ranging from a large uptake to a release of carbon by the terrestrial biosphere, constituting a large uncertainty in the associated feedback to atmospheric CO 2 concentrations under global climate change. Errors and biases that may contribute to such uncertainty include ecosystem model structure, parameters and forcing by climate output from general circulation models (GCMs) or the atmospheric components of Earth system models (ESMs), e.g. as prepared for use in IPCC climate change assessments. The relative importance of these contributing factors to the overall uncertainty in carbon cycle projections is not well characterised. Here we investigate the role of climate model-derived biases by forcing a single global ecosystem-carbon cycle model, with original climate outputs from 15 ESMs and GCMs from the CMIP5 ensemble. We show that variation among the resulting ensemble of present and future carbon cycle simulations propagates from biases in annual means of temperature, precipitation and incoming shortwave radiation. Future changes in carbon pools, and thus land carbon sink trends, are also affected by climate biases, although to a smaller extent than the absolute size of carbon pools. Our results suggest that climate biases could be responsible for a considerable fraction of the large uncertainties in ESM simulations of land carbon fluxes and pools, amounting to about 40% of the range reported for ESMs. We conclude that climate bias-induced uncertainties must be decreased to make accurate coupled atmosphere-carbon cycle projections. (Less)

Abstract: Whether a cloud is predominantly water or ice strongly influences interactions between clouds and radiation coming down from the Sun or up from the Earth. Being able to simulate cloud phase transitions accurately in climate models based on observational data sets is critical in order to improve confidence in climate projections, because this uncertainty contributes greatly to the overall uncertainty associated with cloud-climate feedbacks. Ultimately, it translates into uncertainties in Earth's sensitivity to higher CO2 levels. While a lot of effort has recently been made toward constraining cloud phase in climate models, more remains to be done to document the radiative properties of clouds according to their phase. Here we discuss the added value of a new satellite data set that advances the field by providing estimates of the cloud radiative effect as a function of cloud phase and the implications for climate projections.

Abstract: There is large uncertainty in the simulation of transient climate sensitivity. This study aims to understand how such uncertainty is related to the simulation of the base climate by comparing two simulations with the same model but in which CO2 is increased from either a preindustrial (1860) or a present-day (1990) control simulation. This allows different base climate ocean circulations that are representative of those in current climate models to be imposed upon a single model. As a result, the model projects different transient climate sensitivities that are comparable to the multimodel spread. The greater warming in the 1990-start run occurs primarily at high latitudes and particularly over regions of oceanic convection. In the 1990-start run, ocean overturning circulations are initially weaker and weaken less from CO2 forcing. As a consequence, there are smaller reductions in the poleward ocean heat transport, leading to less tropical ocean heat storage and less moderated high-latitude surfac...

Abstract: Part 1 Introduction: background the factors involved in climate change natural factors affecting climate change nuclear war and climate on the perspective concept and climate change studies. Part 2 The observed regularities of climate: the CO2 cycle and global-scale climate changes from observational data detecting the CO2 signal a global system of observations. Part 3 The World Climate Research Programme WCRP: fundamental principles of the WCRP the Global Energy and Water Cycle Experiment GEWEX. Part 4 Principal climatically-important processes: cloudiness and radiation processes in the ocean the Arctic, the Antarctic and climate land surface processes optically-active minor gaseous compounds aerosols and climate solar-terrestrial interrelations development, verification and application of climate models the comparative climatology of planets. Part 5 The internal variability of the climate system: climate diagnostics the theory of short-period climate changes the sections programme the world ocean and climate nested climate models. Part 6 External impacts on the climactic system: CO2 and climate the multifaceted nature of the atmospheric greenhouse effect volcanoes and climate. Part 7 Conclusion.

Abstract: The expanding interest in decadal climate variability, predictability, and prediction highlights the importance of understanding the sources and mechanisms of decadal and interdecadal climate fluctuations. The purpose of this paper is to provide a critical review of our current understanding of externally forced decadal climate variability. In particular, proposed mechanisms determining decadal climate responses to variations in solar activity, stratospheric volcanic aerosols, and natural as well as anthropogenic tropospheric aerosols are discussed, both separately and in a unified framework. The review suggests that the excitation of internal modes of interdecadal climate variability, particularly centered in the Pacific and North Atlantic sectors, remains a paradigm to characterize externally forced decadal climate variability and to interpret the associated dynamics. Significant recent advancements are the improved understanding of the critical dependency of volcanically forced decadal climate variability on the relative phase of ongoing internal variability and on additional external perturbations, and the recognition that associated uncertainty may represent a serious obstacle to identifying the climatic consequences even of very strong eruptions. Particularly relevant is also the recent development of hypotheses about potential mechanisms (reemergence and synchronization) underlying solar forced decadal climate variability. Finally, outstanding issues and, hence, major opportunities for progress regarding externally forced decadal climate variability are discussed. Uncertain characterization of forcing and climate histories, imperfect implementation of complex forcings in climate models, limited understanding of the internal component of interdecadal climate variability, and poor quality of its simulation are some of the enduring critical obstacles on which to progress. It is suggested that much further understanding can be gained through identification and investigation of relevant periods of forced decadal climate variability during the preindustrial past millennium. Another upcoming opportunity for progress is the analysis of focused experiments with coupled ocean–atmosphere general circulation models within the umbrella of the next phase of the coupled model intercomparison project.

Abstract: Climate model projections are used to investigate the potential impacts of climate change on future weather, agriculture, water resources, human health, the global economy, etc. However, climate projections have a broad range of associated uncertainties, and it is a challenge to take account of these uncertainties in impact studies and risk assessments. Knowing which uncertainties matter and which may be reduced via scientific research or political decisions can help policy-makers in making informed decisions, scientists in focusing their resources, and businesses in building resilience to uncertainties that cannot be avoided. On the global scale, the present political resistance or ability to move from agreements to significant action provides the largest uncertainty in climate projections, followed by the uncertainty associated with climate modelling itself. Here, we show that climate sensitivity is a very important source of model uncertainty over large parts of the globe not only for temperatu...

Abstract: The 2015 Paris Climate Conference elicited largely independent and individual commitments from the participating countries (so-called intended nationally determined contributions) in an effort to c...

Abstract: The projected warming of surface air temperature at the global and regional scale by the end of the century is directly related to emissions and Earth’s climate sensitivity. Projections are typically produced using an ensemble of climate models such as CMIP5, however the range of climate sensitivity in models doesn’t cover the entire range considered plausible by expert judgment. Of particular interest from a risk-management perspective is the lower impact outcome associated with low climate sensitivity and the low-probability, high-impact outcomes associated with the top of the range. Here we scale climate model output to the limits of expert judgment of climate sensitivity to explore these limits. This scaling indicates an expanded range of projected change for each emissions pathway, including a much higher upper bound for both the globe and Australia. We find the possibility of exceeding a warming of 2 °C since pre-industrial is projected under high emissions for every model even scaled to the lowest estimate of sensitivity, and is possible under low emissions under most estimates of sensitivity. Although these are not quantitative projections, the results may be useful to inform thinking about the limits to change until the sensitivity can be more reliably constrained, or this expanded range of possibilities can be explored in a more formal way. When viewing climate projections, accounting for these low-probability but high-impact outcomes in a risk management approach can complement the focus on the likely range of projections. They can also highlight the scale of the potential reduction in range of projections, should tight constraints on climate sensitivity be established by future research.

Abstract: Solar climate engineering — intentional modification of the planet’s reflectivity — is coming under increasing consideration as a means to counter climate change. At present, it offers the possibility of greatly reducing climate risks, but would pose physical and social risks of its own. This chapter offers an introduction to solar climate engineering, exploring its potential, risks, and legal and regulatory challenges. It also contextualizes these proposals with respect to other emerging technologies and the broader socio-political milieu. The contours of existing and potential regulation, particularly at the international level, are explored. These aspects include regulatory rationales, diverse characteristics of proposed regulatory regimes, difficulties in defining the regulatory target, and the management of uncertainty through precaution. The chapter closes with suggested future research directions in the law and regulation of solar climate engineering.

Abstract: Multiple lines of observational evidence indicate that the global climate has been getting warmer since the early 20th century This warmer climate has led to a global mean sea level rise of about 18 cm during the 20th century, and over 6 cm for the first 15 years of the 21st century Regionally the sea level rise is not uniform due in large part to internal climate variability To better serve the community, the uncertainties of predicting/projecting regional sea level changes associated with internal climate variability need to be quantified Previous research on this topic has used single-model large ensembles with perturbed atmospheric initial conditions (ICs) Here we compare uncertainties associated with perturbing ICs in just the atmosphere and just the ocean using a state-of-the-art coupled climate model We find that by perturbing the oceanic ICs, the uncertainties in regional sea level changes increase compared to those with perturbed atmospheric ICs Thus, in order for us to better assess the full spectrum of the impacts of such internal climate variability on regional and global sea level rise, approaches that involve perturbing both atmospheric and oceanic initial conditions are necessary

Abstract: Despite the well-recognized role of water in transmitting climate impacts to some of the growth drivers of the economy, the water sector has been largely ignored in climate change deliberations. The impacts are projected to vary regionally, and are likely to include changes in average hydroclimate patterns (precipitation, surface runoff, and stream flow), as well as increases in the probability of extreme events. Climate shocks are likely to impose higher costs than gradual changes in climate averages. Prudent management of water resources will be pivotal in addressing the climate challenge—both for adapting to the effects of climate change as well as for meeting global greenhouse gas mitigation goals. The precise consequences of climate change on the hydrological cycle are uncertain, which makes adaptation especially challenging. Uncertainty regarding impacts is partly a consequence of the limitations of climate models. Despite improvements in climate science, the Global Circulation Models developed to project climate futures generate a wide range of projections that often disagree on both the direction and magnitude of precipitation changes. Furthermore, these models have not been designed to predict changes in the hydrological cycle and lack the precision required for planning and managing water resources. In addition to this, changes in the hydrological cycle imply that future water systems may not resemble the past (non-stationarity), so historic trends as used in engineering designs, no longer serve as a reliable guide for assessing and managing future risks. This study presents an investigation of the impacts of climate change on water resources throughout the world, and specific effects on water dependent sectors of the economy such as urban, energy, and agriculture. The results can be used to illustrate the centrality of water in achieving global climate change goals.

Abstract: The term climate change is growing in preferred use to ‘Global warming’ because it helps to convey that there are other changes in addition to rising temperature. Climate change refers to any significant change in measures of climate (such as temperature, precipitation or wind) lasting for an extended period (decades or longer). Climate change may result from: a) Natural factors, such as changes in the sun’s intensity or slow changes in the Earth’s orbit around the sun. b) Natural process within the climate system (such as changes in ocean circulation) c) Human activities that change the atmosphere’s condition (such as burning fossil fuels) and deforestation, urbanization and industrialization. Climate change is primarily attributable to rise in the atmospheric temperature of the earth. Our atmosphere traps solar radiation and raises the temperature due to the major greenhouse gases such as carbon dioxide, CFCs, nitrous oxide and methane. In some regions of Asia and Africa, the frequency and intensity of droughts have been observed to increase in recent decades. Episodes of EL Nino which creates great storms, have been more frequent persistent and intense since the mid-1970s compared with the previous 100 years. All these are signs that the Earth is ailing. Its climate is changing making it more difficult for mankind to survive. The Earth is losing its equilibrium due to the imbalances created by human activities. Climate change related impacts on human health could lead to displacement of a large number of people creating environment refugees and lead to further health issues. Climate change is an intricate problem which although environmental in nature has consequences for all spheres of existence on planet. It either impacts on or is impacted by global issues including poverty economic development population growth sustainable development and resource management.

Abstract: Environmental protection is an area of major worldwide concern. The fight against global warming is one of the basic tools of environmental policies and legislation. Climate change is considered to be one of the most important environmental issues. This concern reflects the reality: that so much of human activity is sensitive to climate change, and that adapting to current and projected rates of climate change could be very challenging. It also shows that human perturbation of the climate system is essentially irreversible. As we know, climate change is occurring and the climate system is warming. The conclusive evidence leading to this conclusion includes not only the noticeable increases in average global air and ocean temperatures, but also the widespread melting of snow and ice and the overall rise of the global sea level. Climate change deeply impacts nature and population, and represents a long-term shift in weather conditions, identified by changes in temperature, precipitation, winds and many other indicators. Also, climate change can involve both changes in environmental conditions and changes in variability, including extreme events. Both categories of triggering factors – the ones related to natural processes and the ones related to human activity – cause constant climate change, operate on different time scales and are responsible for overall changes in the earth’s climate. In addition to the natural causes of climate change, changes specific to the climate system, such as variations in ocean currents or atmospheric circulation, can also influence the climate. Climate change has brought about severe and possibly permanent alterations to our planet’s geological, biological and ecological systems. All these changes have led to the emergence of large-scale environmental hazards to the health of humans, such as extreme weather, ozone depletion, loss of biodiversity and stresses to food-producing systems

Abstract: Global warming can result in the rise of Sea Level (SL) by 40–100 cm by the end of the XXI century with possible catastrophic consequences for coastal zone. Study and prediction of long-term fluctuations of sea level is among the most important problems of modern hydrometeorology. A series of studies of SL interannual fluctuations have been carried out in RSHU. A reconstruction of SL fluctuations during the observation period of 1861-2010, i.e. 150 years, was performed on the basis of the developed statistical model showing a powerful linear trend describing 94% of the initial row dispersion. During the XX century the trend approached 1.8 mm/year. The comparison of actual and calculated SL trends for two periods (1980–2005 and 1993-2003) has shown that the residual error makes respectively 0.21 and 0.22 mm/year that is three times less, than in the Fourth IPCC report. Also, for the first time the complex of methods of SL longterm forecast was developed: the main advantage of a simple statistical model of SL longterm forecast is a minimum of initial information, but the model accuracy is comparable with complex and expensive ocean and atmosphere circulation models. The two-decade range physical-statistical sea level prediction model was developed for the first time based on the idea that Global Air Temperature (GAT) is a major factor of SL changes. It was experimentally shown that there is a long delay (20 and 30 years) of SL fluctuations with respect to Global Air Temperature.

Abstract: This chapter explains the physics of climate change, including the greenhouse effect and climate feedbacks, as a prelude to discussing assessments of global warming by the Intergovernmental Panel on Climate Change (IPCC). The critical importance of methane leakage by the oil and gas industry to near-term climate change mitigation is discussed, including estimates of site-specific, regional, and global leakage rates based on observational studies using both top-down and bottom-up measurement approaches. The role of super-emitting facilities in quantifying methane leakage is emphasized. Efforts by the World Bank to reduce global flaring of natural gas associated with oil production, and the possible contribution of the oil and gas industry to increased radiative forcing by tropospheric ozone are also discussed.