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Over the past two decades, the United Nations, the World Bank, regional development banks, and national governments have led efforts to give more people access to electricity. The movement has [...]

Net anthropogenic emissions of carbon dioxide (CO.sub.2) must approach zero by mid-century (2050) in order to stabilize the global mean temperature at the level targeted by international efforts.sup.1-5. Yet continued expansion of fossil-fuel-burning energy infrastructure implies already 'committed' future CO.sub.2 emissions.sup.6-13. Here we use detailed datasets of existing fossil-fuel energy infrastructure in 2018 to estimate regional and sectoral patterns of committed CO.sub.2 emissions, the sensitivity of such emissions to assumed operating lifetimes and schedules, and the economic value of the associated infrastructure. We estimate that, if operated as historically, existing infrastructure will cumulatively emit about 658 gigatonnes of CO.sub.2 (with a range of 226 to 1,479 gigatonnes CO.sub.2, depending on the lifetimes and utilization rates assumed). More than half of these emissions are predicted to come from the electricity sector; infrastructure in China, the USA and the 28 member states of the European Union represents approximately 41 per cent, 9 per cent and 7 per cent of the total, respectively. If built, proposed power plants (planned, permitted or under construction) would emit roughly an extra 188 (range 37-427) gigatonnes CO.sub.2. Committed emissions from existing and proposed energy infrastructure (about 846 gigatonnes CO.sub.2) thus represent more than the entire carbon budget that remains if mean warming is to be limited to 1.5 degrees Celsius (°C) with a probability of 66 to 50 per cent (420-580 gigatonnes CO.sub.2).sup.5, and perhaps two-thirds of the remaining carbon budget if mean warming is to be limited to less than 2 °C (1,170-1,500 gigatonnes CO.sub.2).sup.5. The remaining carbon budget estimates are varied and nuanced.sup.14,15, and depend on the climate target and the availability of large-scale negative emissions.sup.16. Nevertheless, our estimates suggest that little or no new CO.sub.2-emitting infrastructure can be commissioned, and that existing infrastructure may need to be retired early (or be retrofitted with carbon capture and storage technology) in order to meet the Paris Agreement climate goals.sup.17. Given the asset value per tonne of committed emissions, we suggest that the most cost-effective premature infrastructure retirements will be in the electricity and industry sectors, if non-emitting alternatives are available and affordable.sup.4,18. A comprehensive assessment of 'committed' carbon dioxide emissions--from existing and proposed fossil-fuel-based infrastructure--finds that these emissions may exceed the level required to keep global warming within 1.5 degrees Celsius., Author(s): Dan Tong [sup.1] [sup.2] , Qiang Zhang [sup.2] , Yixuan Zheng [sup.2] [sup.3] , Ken Caldeira [sup.3] , Christine Shearer [sup.4] , Chaopeng Hong [sup.1] , Yue Qin [sup.1] [...]

Climate models provide the principal means of projecting global warming over the remainder of the twenty-first century but modelled estimates of warming vary by a factor of approximately two even under the same radiative forcing scenarios. Across-model relationships between currently observable attributes of the climate system and the simulated magnitude of future warming have the potential to inform projections. Here we show that robust across-model relationships exist between the global spatial patterns of several fundamental attributes of Earths top-of-atmosphere energy budget and the magnitude of projected global warming. When we constrain the model projections with observations, we obtain greater means and narrower ranges of future global warming across the major radiative forcing scenarios, in general. In particular, we find that the observationally informed warming projection for the end of the twenty-first century for the steepest radiative forcing scenario is about 15 per cent warmer (+0.5 degrees Celsius) with a reduction of about a third in the two-standard-deviation spread (1.2 degrees Celsius) relative to the raw model projections reported by the Intergovernmental Panel on Climate Change. Our results suggest that achieving any given global temperature stabilization target will require steeper greenhouse gas emissions reductions than previously calculated., Author(s): Patrick T. Brown (corresponding author) [1]; Ken Caldeira [1] Many relevant impacts of global climate change are expected to scale with the change in global mean surface air temperature [...]

Author(s): Patrick T. Brown [sup.1] , Martin B. Stolpe [sup.2] , Ken Caldeira [sup.1] Author Affiliations:(1) Department of Global Ecology, Carnegie Institution for Science, Stanford, USA(2) Institute for Atmospheric and [...]

Approximately one-quarter of the anthropogenic carbon dioxide released into the atmosphere each year is absorbed by the global oceans, causing measurable declines in surface ocean pH, carbonate ion concentration ([C[O.sub.3.sup.2-]), [...]

Letter to the Editor, Author(s): Ken Caldeira, Ian McKay Author Affiliations: Contrails: tweaking flight altitude could be a climate win By our calculation, preventing most of the damaging impact of aircraft vapour trails (contrails) [...]

Author(s): Rebecca Albright (corresponding author) [1, 2]; Yuichiro Takeshita [1, 3]; David A. Koweek [1]; Aaron Ninokawa [4]; Kennedy Wolfe [5]; Tanya Rivlin [6, 7]; Yana Nebuchina [1]; Jordan Young [...]

Like it or not, a climate emergency is a possibility, and geoengineering could be the only affordable and fast-acting option to avoid a global catastrophe. Climate change triggered by the [...]

Slowing climate change requires overcoming inertia in political, technological, and geophysical systems. Of these, only geophysical warming commitment has been quantified. We estimated the commitment to future emissions and warming represented by existing carbon dioxide--emitting devices. We calculated cumulative future emissions of 496 (282 to 701 in lower- and upperbounding scenarios) gigatonnes of C[O.sub.2] from combustion of fossil fuels by existing infrastructure between 2010 and 2060, forcing mean warming of 1.3[degrees]C (1.1[degrees] to 1.4[degrees]C) above the pre-industrial era and atmospheric concentrations of C02 less than 430 parts per million. Because these conditions would likely avoid many key impacts of climate change, we conclude that sources of the most threatening emissions have yet to be built. However, C[O.sub.2]-emitting infrastructure will expand unless extraordinary efforts are undertaken to develop alternatives. 10.1126/science.1188566

An increase in atmospheric carbon dioxide (C[O.sub.2]) concentration influences climate both directly through its radiative effect (i.e., trapping longwave radiation) and indirectly through its physiological effect (i.e., reducing transpiration of land plants). Here we compare the climate response to radiative and physiological effects of increased C[O.sub.2] using the National Center for Atmospheric Research (NCAR) coupled Community Land and Community Atmosphere Model. In response to a doubling oft C[O.sub.2], the radiative effect of C[O.sub.2] causes mean surface air temperature over land to increase by 2.86 [+ or -] 0.02 K ([+ or -]1 standard error), whereas the physiological effects of C[O.sub.2] on land plants alone causes air temperature over land to increase by 0.42 [+ or -] 0.02 K. Combined, these two effects cause a land surface warming of 3.33 [+ or -] 0.03 K. The radiative effect of doubling C[O.sub.2] increases global runoff by 5.2 [+ or -] 0.6 %, primarily by increasing precipitation over the continents. The physiological effect increases runoff by 8.4 [+ or -] 0.6%, primarily by diminishing evapotranspiration from the continents. Combined, these two effects cause a 14.9 [+ or -] 0.7% increase in runoff. Relative humidity remains roughly constant in response to C[O.sub.2]-radiative forcing, whereas relative humidity over land decreases in response to C[O.sub.2]-physiological forcing as a result of reduced plant transpiration. Our study points to an emerging consensus that the physiological effects of increasing atmospheric C[O.sub.2] on land plants will increase global warming beyond that caused by the radiative effects of C[O.sub.2]. global warming | runoff | evapotranspiration | hydrological cycle | plant stomata www.pnas.org/cgi/doi/10.1073/pnas.0913000107

C[O.sub.2] emissions from the burning of fossil fuels are the primary cause of global warming. Much attention has been focused on the C[O.sub.2] directly emitted by each country, but relatively little attention has been paid to the amount of emissions associated with the consumption of goods and services in each country. Consumption-based accounting of C[O.sub.2] emissions differs from traditional, production-based inventories because of imports and exports of goods and services that, either directly or indirectly, involve C[O.sub.2] emissions. Here, using the latest available data, we present a global consumption-based C[O.sub.2] emissions inventory and calculations of associated consumption-based energy and carbon intensities. We find that, in 2004, 23% of global C[O.sub.2] emissions, or 6.2 gigatonnes C[O.sub.2], were traded internationally, primarily as exports from China and other emerging markets to consumers in developed countries, in some wealthy countries, including Switzerland, Sweden, Austria, the United Kingdom, and France, >30% of consumption-based emissions were imported, with net imports to many Europeans of >4 tons C[O.sub.2] per person in 2004. Net import of emissions to the United States in the same year was somewhat less: 10.8% of total consumption-based emissions and 2.4 tons C[O.sub.2] per person. In contrast, 22.5% of the emissions produced in China in 2004 were exported, on net, to consumers elsewhere. Consumption-based accounting of C[O.sub.2] emissions demonstrates the potential for international carbon leakage. Sharing responsibility for emissions among producers and consumers could facilitate international agreement on global climate policy that is now hindered by concerns over the regional and historical inequity of emissions. carbon intensity of economy | carbon intensity of energy | emissions embodied in trade | fossil fuels | Kaya identity www.pnas.org/cgi/doi/10.1073/pnas.0906974107

Environmental conditions during the past 24 million years are thought to have been favourable for enhanced rates of atmospheric carbon dioxide drawdown by silicate chemical weathering (1-7). Proxy records indicate, however, that the Earth's atmospheric carbon dioxide concentrations did not fall below about 200-250 parts per million during this period (8). The stabilization of atmospheric carbon dioxide concentrations near this minimum value suggests that strong negative feedback mechanisms inhibited further drawdown of atmospheric carbon dioxide by high rates of global silicate rock weathering. Here we investigate one possible negative feedback mechanism, occurring under relatively low carbon dioxide concentrations and in warm climates, that is related to terrestrial plant productivity and its role in the decomposition of silicate minerals9-11. We use simulations of terrestrial and geochemical carbon cycles and available experimental evidence to show that vegetation activity in upland regions of active orogens was severely limited by near-starvation of carbon dioxide in combination with global warmth over this period. These conditions diminished biotic-driven silicate rock weathering and thereby attenuated an important long-term carbon dioxide sink. Although our modelling results are semi-quantitative and do not capture the full range of biogeochemical feedbacks that could influence the climate, our analysis indicates that the dynamic equilibrium between plants, climate and the geosphere probably buffered the minimum atmospheric carbon dioxide concentrations over the past 24 million years., Alkenone-based proxy records8 indicate that atmospheric carbon dioxide (C[O.sub.2]) concentrations ranged between 1,000 and 1,500 parts per million (p.p.m.) from about 45 to 34 million years (Myr) ago (the middle [...]

Geoengineering (the intentional modification of Earth's climate) has been proposed as a means of reducing C[O.sub.2]-induced climate warming while greenhouse gas emissions continue. Most proposals involve managing incoming solar radiation such that future greenhouse gas forcing is counteracted by reduced solar forcing. In this study, we assess the transient climate response to geoengineering under a business-as-usual C[O.sub.2] emissions scenario by using an intermediate-complexity global climate model that includes an interactive carbon cycle. We find that the climate system responds quickly to artificially reduced insolation; hence, there may be little cost to delaying the deployment of geoengineering strategies until such a time as 'dangerous' climate change is imminent. Spatial temperature patterns in the geoengineered simulation are comparable with preindustrial temperatures, although this is not true for precipitation. Carbon sinks in the model increase in response to geoengineering. Because geoengineering acts to mask climate warming, there is a direct C[O.sub.2]-driven increase in carbon uptake without an offsetting temperature-driven suppression of carbon sinks. However, this strengthening of carbon sinks, combined with the potential for rapid climate adjustment to changes in solar forcing, leads to serious consequences should geoengineering fail or be stopped abruptly. Such a scenario could lead to very rapid climate change, with warming rates up to 20 times greater than present-day rates. This warming rebound would be larger and more sustained should climate sensitivity prove to be higher than expected. Thus, employing geoengineering schemes with continued carbon emissions could lead to severe risks for the global climate system. carbon cycle | climate change | geoengineering | climate forcing | managing solar radiation

The evolutionary success of planktic calcifiers during the Phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate-ion concentration: the saturation-dependent preservation of carbonate in sea-floor sediments. Before this, buffering was primarily accomplished by adjustment of shallow-water carbonate deposition to balance oceanic inputs from weathering on land. Neoproterozoic ice ages of near-global extent and multimillion-year duration and the formation of distinctive sedimentary (cap) carbonates can thus be understood in terms of the greater sensitivity of the Precambrian carbon cycle to the loss of shallow-water environments and C[O.sup.2]-climate feedback on ice-sheet growth., The growth of continental-scale ice sheets extending to the tropics during the second half of the Neoprotemzoic (1000 to 540 million years ago) (1) is now widely accepted in the [...]

Stabilizing the carbon dioxide-induced component of climate change is an energy problem. Establishment of a course toward such stabilization will require the development within the coming decades of primary energy sources that do not emit carbon dioxide to the atmosphere, in addition to efforts to reduce end-use energy demand. Mid-century primary power requirements that are free of carbon dioxide emissions could be several times what we now derive from fossil fuels (~[10.sup.13] watts), even with improvements in energy efficiency. Here we survey possible future energy sources, evaluated for their capability to supply massive amounts of carbon emission-free energy and for their potential for large-scale commercialization. Possible candidates for primary energy sources include terrestrial solar and wind energy, solar power satellites, biomass, nuclear fission, nuclear fusion, fission-fusion hybrids, and fossil fuels from which carbon has been sequestered. Non-primary power technologies that could contribute to climate stabilization include efficiency improvements, hydrogen production, storage and transport, superconducting global electric grids, and geoengineering. All of these approaches currently have severe deficiencies that limit their ability to stabilize global climate. We conclude that a broad range of intensive research and development is urgently needed to produce technological options that can allow both climate stabilization and economic development., More than a century ago, Arrhenius put forth the idea that C[O.sub.2] from fossil fuel burning could raise the infrared opacity of the atmosphere enough to warm Earth (1). In [...]

The United Nations (UN) has called for greenhouse gas concentration to be stabilized in its Convention on Climate Change, in order to prevent global warming. Stabilization will need cost-effective and innovative technology if economic growth is to continue, and this is true even if the productivity of primary energy is improved on a sustained basis. The lower the emission targets, the more carbon-emission-free power will be needed. There is a need for large investments in energy research due to the major challenge involved in infrastructure transition.

In their article 'Comparative Earth history and Late Permian mass extinction' (1), A. H. Knoll et al. suggest that Late Permian extinctions were caused by the release to the atmosphere [...]

The UN Framework Convention on Climate Change calls for 'stabilization of greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interference with the climate system.' Even if we could determine a 'safe' level of interference in the climate system, the sensitivity of global mean temperature to increasing atmospheric C[O.sub.2] is known perhaps only to a factor of three or less. Here we show how a factor of three uncertainty in climate sensitivity introduces even greater uncertainty in allowable increases in atmospheric C[O.sub.2] concentration and allowable C[O.sub.2] emissions. Nevertheless, unless climate sensitivity is low and acceptable amounts of climate change are high, climate stabilization will require a massive transition to C[O.sub.2] emission-free energy technologies., Climate sensitivity (Δ[T.sub.2X]) is the global mean climatological temperature change resulting from a doubling of atmospheric C[O.sub.2] content. Climate sensitivity is thought, based primarily on models, to lie in the [...]

Carbon dioxide emission scenarios do not influence the global warming potential of CO2 with respect to other radioactive trace gases. Six scenarios are examined to indicate that atmospheric CO2 concentration is inversely proportional to the variation in climate. The sea absorbs less CO2 from the atmosphere due to increased concentrations of dissolved carbon in the sea's surface.

As the luminosity of the sun increases and warms the earth, atmospheric carbon dioxide will eventually decrease below the level necessary for photosynthesis and life will end on the Earth. The decrease in atmospheric carbon dioxide (CO2) is caused by the increased weathering of silicate rocks, which is induced by the raised temperature. A model incorporating the greenhouse effect and the photosynthesis requirements of C4 plants predicts that the biosphere will last another 0.9 to 1.5 billion years, depending on whether increased temperature or decreased CO2 is the deciding factor.

The warming of the Earth soon after it formed probably prevented the onset of an interminable glacial climate due to highly reflective carbon dioxide (CO2) clouds and the Sun's much less intense output of heat at the time. The suggestion that an early greenhouse effect stabilized the Earth's climate does not explain why the oceans failed to freeze before the greenhouse gases could accumulate. Paleoclimatic simulations indicate that Earth may have narrowly escaped being rendered uninhabitable by world-wide glaciation thanks to either internal heat or additional greenhouse gases.

An ocean-climate model that shows high fluxes of anthropogenic carbon dioxide into the Southern Ocean, but very low storage of anthropogenic carbon there, agrees with observation-based estimates of ocean storage of anthropogenic carbon dioxide. This low simulated storage indicates a subordinate role for deep convection in the present-day Southern Ocean. The primary mechanism transporting anthropogenic carbon out of the Southern Ocean is isopycnal transport. These results imply that if global climate change reduces the density of surface waters in the Southern Ocean, isopycnal surfaces that now outcrop may become isolated from the atmosphere, tending to diminish Southern Ocean carbon uptake., There has been considerable debate (1, 2) about the importance of Southern Ocean uptake of anthropogenic [CO.sub.2]. Several modeling studies (2-6) have indicated a relatively large Southern Ocean sink for [...]

The hypothesis that the rise of the Tibetan plateau helped to lower global temperatures by increasing the quantity of carbon dioxide(CO2)-absorbing silicate rock is questionable. The numerical data underlying this hypothesis are incomplete. Moreover, the implication that CO2 fluctuations are linked to geological weathering is unproven. However, the rebuttal view is that some carbon cycle models do relate to silicate and carbonate weathering. The hypothesis agrees well with the geological data.

Author(s): Ken Caldeira (corresponding author) [1]; Michael E. Wickett [2] Most carbon dioxide released into the atmosphere as a result of the burning of fossil fuels will eventually be absorbed [...]

Author(s): Ken Caldeira [1] Sir To understand why many physical scientists regard economists with scepticism, one need look no further than the Concepts essay on discounting ('An eye on the [...]

The views of E.N. Parker on the potential impact on terrestrial climate, published with the paper on solar variability of M. Lockwood and others are inaccurate and out of line with Lockwood's evidence. Parker's suggestion that solar brightening causes an increase in carbon dioxide levels comparable with the expulsion of carbon dioxide from a warm carbonated drink is exaggerated.