In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of t...In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature.Half of these estimates are"low variability"and half are"high variability".Meanwhile,five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using:1)only rural weather stations;2)all available stations whether urban or rural(the standard approach);3)only sea surface temperatures;4)tree-ring widths as temperature proxies;5)glacier length records as temperature proxies.The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates,suggesting that urbanization bias might still be a problem in current global temperature datasets-despite the conclusions of some earlier studies.Nonetheless,all five estimates confirm that it is currently warmer than the late 19th century,i.e.,there has been some"global warming"since the 19th century.For each of the five estimates of Northern Hemisphere temperatures,the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting.The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended"anthropogenic forcings"time series.For all five Northern Hemisphere temperature series,different TSI estimates suggest everything from no role for the Sun in recent decades(implying that recent global warming is mostly human-caused)to most of the recent global warming being due to changes in solar activity(that is,that recent global warming is mostly natural).It appears that previous studies(including the most recent IPCC reports)which had prematurely concluded the former,had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates.Therefore,several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.展开更多
Since 2007,the Intergovernmental Panel on Climate Change(IPCC)has heavily relied on the comparison between global climate model hindcasts and global surface temperature(ST)estimates for concluding that post-1950s glob...Since 2007,the Intergovernmental Panel on Climate Change(IPCC)has heavily relied on the comparison between global climate model hindcasts and global surface temperature(ST)estimates for concluding that post-1950s global warming is mostly human-caused.In Connolly et al.,we cautioned that this approach to the detection and attribution of climate change was highly dependent on the choice of Total Solar Irradiance(TSI)and ST data sets.We compiled 16 TSI and five ST data sets and found by altering the choice of TSI or ST,one could(prematurely)conclude anything from the warming being“mostly human-caused”to“mostly natural.”Richardson and Benestad suggested our analysis was“erroneous”and“flawed”because we did not use a multilinear regression.They argued that applying a multilinear regression to one of the five ST series re-affirmed the IPCC's attribution statement.They also objected that many of the published TSI data sets were out-of-date.However,here we show that when applying multilinear regression analysis to an expanded and updated data set of 27 TSI series,the original conclusions of Connolly et al.are confirmed for all five ST data sets.Therefore,it is still unclear whether the observed warming is mostly human-caused,mostly natural or some combination of both.展开更多
The IPCC AR6 assessment of the impacts and risks associated with projected climate changes for the 21st century is both alarming and ambiguous.According to computer projections,global surface temperature may warm from...The IPCC AR6 assessment of the impacts and risks associated with projected climate changes for the 21st century is both alarming and ambiguous.According to computer projections,global surface temperature may warm from 1.3℃to 8.0℃by 2100,depending on the global climate model(GCM)and the shared socioeconomic pathway(SSP)scenario used for the simulations.Actual climate-change hazards are estimated to be high and very high if the global surface temperature rises,respectively,more than 2.0℃and 3.0℃above pre-industrial levels.Recent studies,however,showed that a substantial number of CMIP6 GCMs run“too hot”because they appear to be too sensitive to radiative forcing,and that the high/extreme emission scenarios SSP3-7.0 and SSP5-8.5 are to be rejected because judged to be unlikely and highly unlikely,respectively.Yet,the IPCC AR6 mostly focused on such alarmistic scenarios for risk assessments.This paper examines the impacts and risks of“realistic”climate change projections for the 21st century generated by assessing the theoretical models and integrating them with the existing empirical knowledge on global warming and the various natural cycles of climate change that have been recorded by a variety of scientists and historians.This is achieved by combining the SSP2-4.5 scenario(which is the most likely SSP according to the current policies reported by the International Energy Agency)and empirically optimized climate modeling.According to recent research,the GCM macro-ensemble that best hindcast the global surface warming observed from 1980 to 1990 to 2012–2022 should be made up of models that are characterized by a low equilibrium climate sensitivity(ECS)(1.5℃<ECS≤3.0℃),in contrast to the IPCC AR6 likely and very likely ECS ranges at 2.5–4.0℃and 2.0–5.0℃,respectively.I show that the low-ECS macro-GCM with the SSP2-4.5 scenario projects a global surface temperature warming of 1.68–3.09℃by 2080–2100 instead of 1.98–3.82℃obtained with the GCMs with ECS in the 2.5–4.0℃range.However,if the global surface temperature records are affected by significant non-climatic warm biases—as suggested by satellite-based lower troposphere temperature records and current studies on urban heat island effects—the same climate simulations should be scaled down by about 30%,resulting in a warming of about 1.18–2.16℃by 2080–2100.Furthermore,similar moderate warming estimates(1.15–2.52℃)are also projected by alternative empirically derived models that aim to recreate the decadal-to-millennial natural climatic oscillations,which the GCMs do not reproduce.The proposed methodologies aim to simulate hypothetical models supposed to optimally hindcast the actual available data.The obtained climate projections show that the expected global surface warming for the 21st-century will likely be mild,that is,no more than 2.5–3.0℃and,on average,likely below the 2.0℃threshold.This should allow for the mitigation and management of the most dangerous climate-change related hazards through appropriate low-cost adaptation policies.In conclusion,enforcing expensive decarbonization and net-zero emission scenarios,such as SSP1-2.6,is not required because the Paris Agreement temperature target of keeping global warming<2℃throughout the 21st century should be compatible also with moderate and pragmatic shared socioeconomic pathways such as the SSP2-4.5.展开更多
The role of the Sun in climate change is hotly debated.Some studies suggest its impact is significant,while others suggest it is minimal.The Intergovernmental Panel on Climate Change(IPCC)supports the latter view and ...The role of the Sun in climate change is hotly debated.Some studies suggest its impact is significant,while others suggest it is minimal.The Intergovernmental Panel on Climate Change(IPCC)supports the latter view and suggests that nearly 100%of the observed surface warming from 1850–1900 to 2020 is due to anthropogenic emissions.However,the IPCC’s conclusions are based solely on computer simulations made with global climate models(GCMs)forced with a total solar irradiance(TSI)record showing a low multi-decadal and secular variability.The same models also assume that the Sun affects the climate system only through radiative forcing–such as TSI–even though the climate could also be affected by other solar processes.In this paper I propose three“balanced”multi-proxy models of total solar activity(TSA)that consider all main solar proxies proposed in scientific literature.Their optimal signature on global and sea surface temperature records is assessed together with those produced by the anthropogenic and volcanic radiative forcing functions adopted by the CMIP6 GCMs.This is done by using a basic energy balance model calibrated with a differential multi-linear regression methodology,which allows the climate system to respond to the solar input differently than to radiative forcings alone,and to evaluate the climate’s characteristic time-response as well.The proposed methodology reproduces the results of the CMIP6 GCMs when their original forcing functions are applied under similar physical conditions,indicating that,in such a scenario,the likely range of the equilibrium climate sensitivity(ECS)could be 1.4℃to 2.8℃,with a mean of 2.1℃(using the HadCRUT5 temperature record),which is compatible with the low-ECS CMIP6 GCM group.However,if the proposed solar records are used as TSA proxies and the climatic sensitivity to them is allowed to differ from the climatic sensitivity to radiative forcings,a much greater solar impact on climate change is found,along with a significantly reduced radiative effect.In this case,the ECS is found to be 0.9–1.8℃,with a mean of around 1.3℃.Lower ECS ranges(up to 20%)are found using HadSST4,HadCRUT4,and HadSST3.The result also suggests that at least about 80%of the solar influence on the climate may not be induced by TSI forcing alone,but rather by other Sun-climate processes(e.g.,by a solar magnetic modulation of cosmic ray and other particle fluxes,and/or others),which must be thoroughly investigated and physically understood before trustworthy GCMs can be created.This result explains why empirical studies often found that the solar contribution to climate changes throughout the Holocene has been significant,whereas GCM-based studies,which only adopt radiative forcings,suggest that the Sun plays a relatively modest role.展开更多
基金financial support from the Center for Environmental Research and Earth Sciences(CERES)support from NASA+2 种基金NSFTennessee State Universitythe State of Tennessee through its Centers of Excellence program。
文摘In order to evaluate how much Total Solar Irradiance(TSI)has influenced Northern Hemisphere surface air temperature trends,it is important to have reliable estimates of both quantities.Sixteen different estimates of the changes in TSI since at least the 19th century were compiled from the literature.Half of these estimates are"low variability"and half are"high variability".Meanwhile,five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using:1)only rural weather stations;2)all available stations whether urban or rural(the standard approach);3)only sea surface temperatures;4)tree-ring widths as temperature proxies;5)glacier length records as temperature proxies.The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates,suggesting that urbanization bias might still be a problem in current global temperature datasets-despite the conclusions of some earlier studies.Nonetheless,all five estimates confirm that it is currently warmer than the late 19th century,i.e.,there has been some"global warming"since the 19th century.For each of the five estimates of Northern Hemisphere temperatures,the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting.The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC’s recommended"anthropogenic forcings"time series.For all five Northern Hemisphere temperature series,different TSI estimates suggest everything from no role for the Sun in recent decades(implying that recent global warming is mostly human-caused)to most of the recent global warming being due to changes in solar activity(that is,that recent global warming is mostly natural).It appears that previous studies(including the most recent IPCC reports)which had prematurely concluded the former,had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates.Therefore,several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.
基金financial support from the Center for Environmental Research and Earth Sciences(CERES,www.ceres-science.com)while carrying out the research for this paperlong-term support from NASA,NSF,Tennessee State University,and the State of Tennessee through its Centers of Excellence Programthe support of the grant PID-5265TC of the National Technological University of Argentina。
文摘Since 2007,the Intergovernmental Panel on Climate Change(IPCC)has heavily relied on the comparison between global climate model hindcasts and global surface temperature(ST)estimates for concluding that post-1950s global warming is mostly human-caused.In Connolly et al.,we cautioned that this approach to the detection and attribution of climate change was highly dependent on the choice of Total Solar Irradiance(TSI)and ST data sets.We compiled 16 TSI and five ST data sets and found by altering the choice of TSI or ST,one could(prematurely)conclude anything from the warming being“mostly human-caused”to“mostly natural.”Richardson and Benestad suggested our analysis was“erroneous”and“flawed”because we did not use a multilinear regression.They argued that applying a multilinear regression to one of the five ST series re-affirmed the IPCC's attribution statement.They also objected that many of the published TSI data sets were out-of-date.However,here we show that when applying multilinear regression analysis to an expanded and updated data set of 27 TSI series,the original conclusions of Connolly et al.are confirmed for all five ST data sets.Therefore,it is still unclear whether the observed warming is mostly human-caused,mostly natural or some combination of both.
文摘The IPCC AR6 assessment of the impacts and risks associated with projected climate changes for the 21st century is both alarming and ambiguous.According to computer projections,global surface temperature may warm from 1.3℃to 8.0℃by 2100,depending on the global climate model(GCM)and the shared socioeconomic pathway(SSP)scenario used for the simulations.Actual climate-change hazards are estimated to be high and very high if the global surface temperature rises,respectively,more than 2.0℃and 3.0℃above pre-industrial levels.Recent studies,however,showed that a substantial number of CMIP6 GCMs run“too hot”because they appear to be too sensitive to radiative forcing,and that the high/extreme emission scenarios SSP3-7.0 and SSP5-8.5 are to be rejected because judged to be unlikely and highly unlikely,respectively.Yet,the IPCC AR6 mostly focused on such alarmistic scenarios for risk assessments.This paper examines the impacts and risks of“realistic”climate change projections for the 21st century generated by assessing the theoretical models and integrating them with the existing empirical knowledge on global warming and the various natural cycles of climate change that have been recorded by a variety of scientists and historians.This is achieved by combining the SSP2-4.5 scenario(which is the most likely SSP according to the current policies reported by the International Energy Agency)and empirically optimized climate modeling.According to recent research,the GCM macro-ensemble that best hindcast the global surface warming observed from 1980 to 1990 to 2012–2022 should be made up of models that are characterized by a low equilibrium climate sensitivity(ECS)(1.5℃<ECS≤3.0℃),in contrast to the IPCC AR6 likely and very likely ECS ranges at 2.5–4.0℃and 2.0–5.0℃,respectively.I show that the low-ECS macro-GCM with the SSP2-4.5 scenario projects a global surface temperature warming of 1.68–3.09℃by 2080–2100 instead of 1.98–3.82℃obtained with the GCMs with ECS in the 2.5–4.0℃range.However,if the global surface temperature records are affected by significant non-climatic warm biases—as suggested by satellite-based lower troposphere temperature records and current studies on urban heat island effects—the same climate simulations should be scaled down by about 30%,resulting in a warming of about 1.18–2.16℃by 2080–2100.Furthermore,similar moderate warming estimates(1.15–2.52℃)are also projected by alternative empirically derived models that aim to recreate the decadal-to-millennial natural climatic oscillations,which the GCMs do not reproduce.The proposed methodologies aim to simulate hypothetical models supposed to optimally hindcast the actual available data.The obtained climate projections show that the expected global surface warming for the 21st-century will likely be mild,that is,no more than 2.5–3.0℃and,on average,likely below the 2.0℃threshold.This should allow for the mitigation and management of the most dangerous climate-change related hazards through appropriate low-cost adaptation policies.In conclusion,enforcing expensive decarbonization and net-zero emission scenarios,such as SSP1-2.6,is not required because the Paris Agreement temperature target of keeping global warming<2℃throughout the 21st century should be compatible also with moderate and pragmatic shared socioeconomic pathways such as the SSP2-4.5.
文摘The role of the Sun in climate change is hotly debated.Some studies suggest its impact is significant,while others suggest it is minimal.The Intergovernmental Panel on Climate Change(IPCC)supports the latter view and suggests that nearly 100%of the observed surface warming from 1850–1900 to 2020 is due to anthropogenic emissions.However,the IPCC’s conclusions are based solely on computer simulations made with global climate models(GCMs)forced with a total solar irradiance(TSI)record showing a low multi-decadal and secular variability.The same models also assume that the Sun affects the climate system only through radiative forcing–such as TSI–even though the climate could also be affected by other solar processes.In this paper I propose three“balanced”multi-proxy models of total solar activity(TSA)that consider all main solar proxies proposed in scientific literature.Their optimal signature on global and sea surface temperature records is assessed together with those produced by the anthropogenic and volcanic radiative forcing functions adopted by the CMIP6 GCMs.This is done by using a basic energy balance model calibrated with a differential multi-linear regression methodology,which allows the climate system to respond to the solar input differently than to radiative forcings alone,and to evaluate the climate’s characteristic time-response as well.The proposed methodology reproduces the results of the CMIP6 GCMs when their original forcing functions are applied under similar physical conditions,indicating that,in such a scenario,the likely range of the equilibrium climate sensitivity(ECS)could be 1.4℃to 2.8℃,with a mean of 2.1℃(using the HadCRUT5 temperature record),which is compatible with the low-ECS CMIP6 GCM group.However,if the proposed solar records are used as TSA proxies and the climatic sensitivity to them is allowed to differ from the climatic sensitivity to radiative forcings,a much greater solar impact on climate change is found,along with a significantly reduced radiative effect.In this case,the ECS is found to be 0.9–1.8℃,with a mean of around 1.3℃.Lower ECS ranges(up to 20%)are found using HadSST4,HadCRUT4,and HadSST3.The result also suggests that at least about 80%of the solar influence on the climate may not be induced by TSI forcing alone,but rather by other Sun-climate processes(e.g.,by a solar magnetic modulation of cosmic ray and other particle fluxes,and/or others),which must be thoroughly investigated and physically understood before trustworthy GCMs can be created.This result explains why empirical studies often found that the solar contribution to climate changes throughout the Holocene has been significant,whereas GCM-based studies,which only adopt radiative forcings,suggest that the Sun plays a relatively modest role.
