Abstract: The climate feedback determines how Earth’s climate responds to anthropogenic forcing. It is thought to have been more negative in recent decades due to a sea surface temperature “pattern effect,” whereby warming is concentrated in the western tropical Pacific, where nonlocal radiative feedbacks are very negative. This phenomenon has however primarily been studied within climate models. We diagnose a pattern effect from historical records as an evolution of the climate feedback over the past five decades. Our analysis assumes a constant rate of change of the climate feedback, which is justified post hoc. We find a decrease in climate feedback by 0.8 ± 0.5 W m−2 K−1 over the past 50 years, corresponding to a reduction in climate sensitivity. Earth system models’ climate feedbacks instead increase over this period. Understanding and simulating this historical trend and its future evolution are critical for reliable climate projections.

Abstract: This article reviews the first to sixth report of the Inter-Governmental Panel on Climate Change (IPCC). The types of greenhouse gases, sources of greenhouse gases and the impact of climate change on man, animals and the environment has been identified. The strategies to combat climate change has been studied in these reports. A review of these reports are necessary and it is an obligatory document required to combat the adverse effects of climate change and global warming.

Abstract: Note: The purpose of this contribution is to initiate awareness of well-known long-term consequences of climate mitigation measures, and as such it is a debating essay rather than a scientific publication. The consequences of climate change are often communicated with reference to a 100-year timescale, even though the timescales of different climate forcing mechanisms vary with several orders of magnitude. In the Intergovernmental Panel on Climate Change (IPCC) assessment reports, a 20-, 100-, and 500-year global warming potential metric has been used to quantify the impact of climate forcers. The United Nations Climate Conferences have adopted the 100-year global warming potential (GWP100y) metrics, and this measure has become the common reference and has as such come to stand alone in the public and political discussions. We demonstrate that the 100-year metric can be misleading and directly harmful to the environment on longer timescales (500–1000 years), when used as reference for political decisions. The basic mechanism being emphasized here is that the 100-year metric weights relatively short-lived anthropogenic climate forcers, such as, for instance, methane and nitrous oxide, unreasonably high in the emission budget. This is especially the case if a fixed emission reduction target has been set prior political negotiations about mitigation policies.

Abstract: Cost-benefit integrated assessment models (IAMs) such as the Dynamic Integrated model of Climate and the Economy (DICE) are often used to assess the social cost of carbon (SCC), the marginal damage arising from each additional ton of emitted CO2. The climate component of such IAMs has recently come under increased scrutiny. Alongside ensuring that economists are getting climate dynamics correct, the uncertainty in the climate system should be embraced, as it greatly influences the appropriate SCC and CO2 emissions mitigation pathway.We use DICE, replacing its native climate module with the Finite-amplitude Impulse Response (FaIR) model (v2.1). FaIR is assessed to be fit-for-purpose for evaluating emissions projections from IAMs by the IPCC, and has an advantage over the native DICE module in that carbon cycle feedbacks are included. The FaIR emulator has been calibrated to CMIP6 models and constrained such that its projections are consistent with historical global mean temperature change, atmospheric CO2 concentration and ocean heat content, and IPCC Sixth Assessment Report assessed uncertainty ranges for equilibrium climate sensitivity (ECS), transient climate response and non-CO2 effective radiative forcing, constructing a 1000-member posterior ensemble from a 1.5 million member prior. Three ensembles are produced: a Nordhaus “socially optimal” ensemble with median 2100 warming of around 2.8°C, somewhat consistent with current Nationally Determined Contributions; a 2°C-consistent ensemble; and a 1.5°C-consistent ensemble. We update the economic and climate baseline in DICE/FaIR to 2023 and use a 3-year model timestep. The three scenarios are constructed solely by modifying the discount rate.The influence of climate uncertainty is profound, having a factor of 5 uncertainty (5-95% range) in the social cost of carbon for a 1.5°C consistent ensemble, and a factor of 3 uncertainty in the business as usual case. There is also a very strong positive correlation between the SCC and the ECS, which re-confirms earlier analysis that reducing climate system uncertainty can realise net present economic benefits by guiding appropriate choices for the SCC. Alongside calculating a SCC for the year 2023, DICE/FaIR computes probabilistic projections of socially “optimal” CO2 pathways for each scenario that also show substantial variation depending on the climate configuration (for example, -14 to +11 GtCO2/yr in 2050 for the 1.5°C ensemble) but are broadly consistent with findings from the IPCC Sixth Assessment Working Group 3 report in the median case (such as global net zero emissions required in the 2050s to meet 1.5°C). The range of socially optimal emissions pathways consistent with a specific temperature threshold also highlights a climate-socioeconomic feedback: if climate sensitivity is high, mitigation efforts must be strong to limit future warming and climate damages. This feedback, while implicitly included in cost-benefit IAMs such as DICE, are not typically present in process-based IAMs used to construct emissions scenarios for use by the IPCC or climate models such as the Shared Socioeconomic Pathways. We claim that including climate and climate uncertainty in these process-based IAMs will improve emissions scenarios.

Abstract: Emissions pathways used in climate policy analysis are often derived from integrated assessment models. However, such emissions pathways do not typically include climate feedbacks on socioeconomic systems and by extension do not consider climate uncertainty in their construction. We use a well-known cost-benefit integrated assessment model, the Dynamic Integrated Climate-Economy (DICE) model, with its climate component replaced by the Finite-amplitude Impulse Response (FaIR) model (v2.1). The climate uncertainty in FaIR is sampled with an ensemble that is consistent with historically observed climate and Intergovernmental Panel on Climate Change (IPCC) assessed ranges of key climate variables such as equilibrium climate sensitivity. Three scenarios are produced: a pathway similar to the "optimal welfare" scenario of DICE that has similar warming outcomes to current policies, and pathways that limit warming to "well-below" 2C and 1.5C with low overshoot, in line with Paris Agreement long-term temperature goals. Climate uncertainty alone is responsible for a factor of five variation (5-95% range) in the social cost of carbon in the 1.5C scenario. CO2 emissions trajectories resulting from the optimal level of emissions abatement in all pathways are also sensitive to climate uncertainty, with 2050 emissions ranging from -12 to +14 GtCO2/yr in the 1.5C scenario. Equilibrium climate sensitivity and the strength of present-day aerosol effective radiative forcing are strong determinants of social cost of carbon and mid-century CO2 emissions. This shows that narrowing climate uncertainty leads to more refined estimates for the social cost of carbon and provides more certainty about the optimal rate of emissions abatement. Including climate and climate uncertainty in integrated assessment model derived emissions scenarios would address a key missing feedback in scenario construction.

Abstract: Abstract. Intergovernmental Panel on Climate Change (IPCC) assessments are the trusted source of scientific evidence for climate negotiations taking place under the United Nations Framework Convention on Climate Change (UNFCCC), including the first global stocktake under the Paris Agreement that will conclude at COP28 in December 2023. Evidence-based decision-making needs to be informed by up-to-date and timely information on key indicators of the state of the climate system and of the human influence on the global climate system. However, successive IPCC reports are published at intervals of 5–10 years, creating potential for an information gap between report cycles. We follow methods as close as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, surface temperature changes, the Earth's energy imbalance, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. The purpose of this effort, grounded in an open data, open science approach, is to make annually updated reliable global climate indicators available in the public domain (https://doi.org/10.5281/zenodo.8000192, Smith et al., 2023a). As they are traceable to IPCC report methods, they can be trusted by all parties involved in UNFCCC negotiations and help convey wider understanding of the latest knowledge of the climate system and its direction of travel. The indicators show that human-induced warming reached 1.14 [0.9 to 1.4] ^∘C averaged over the 2013–2022 decade and 1.26 [1.0 to 1.6] ^∘C in 2022. Over the 2013–2022 period, human-induced warming has been increasing at an unprecedented rate of over 0.2 ^∘C per decade. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 54 ± 5.3 GtCO₂e over the last decade, as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that increases in greenhouse gas emissions have slowed, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track a change of direction for human influence on climate.

Abstract: The currently ongoing climate change and the debate about possible measures to be taken to limit the consequences of climate change, requires to know and understand the future response of the climate system to greenhouse gas emissions. Classical measures of climate change such as the Equilibrium Climate Sensitivity (ECS) are inherently linear and unable to account for abrupt transitions due to (interacting) tipping elements.In this presentation I will discuss more general notions of climate sensitivity defined on a climate attractor that can be useful in understanding the response of a climate state to changes in radiative forcing. For example, a climate state close to a tipping point will have a degenerate linear response to perturbations, which can be associated with extreme values of the ECS. While many identified tipping elements in the climate system are regional and may have no direct impact on the global mean temperature, cascades of tipping elements can potentially have an impact, initiated by the threshold of the leading tipping element in a cascade.

Abstract: "The effects of climate change induced by increasing greenhouse effect due to the human activities have been intensely started to touch our daily lives. Evaluation of the potential effects of climate change on environmental and natural systems is very important for adaptation and mitigation of the effects of climate change. For this reason, how the climate will change within different emission scenarios should be examined and strategies to cope with climate change should be put forward in the light of these expectations. The aim of this article is to reveal the change of climate on a global scale and its reflections especially on Türkiye. In this context, climate scenarios and climate models on which future climate projections are based on, will be examined. Global climate model projections under different scenarios of Shared Socio- Economic Pathways will be presented by focusing on spatial and temporal variations of global average temperatures and precipitation. Future climate projections on Türkiye produced for medium and high emission scenarios using regional climate models will be discussed."

Abstract: <p><strong>Work Package:</strong> WP4</p><p><strong>Deliverable number:</strong> D4.8</p><p><strong>Deliverable title:</strong> KGSIR on knowledge gained in understanding of climate sensitivity and its role in projections</p><p><strong>Key messages:</strong></p><ul><li>Both CO2 and non-CO2 greenhouse gas emissions must be decreased as quickly as possible to maintain a chance of not exceeding the global temperature limits in the Paris Agreement.</li><li>Using historical warming to constrain future climate projections, we narrow down the uncertainty in climate sensitivity and projected warming by 30-50%.</li><li>We provide a framework to estimate the remaining carbon budget that enables taking into account uncertainties in climate sensitivity and other feedbacks.</li><li>The median estimate for the remaining carbon budget given a 1.5°C limit was 440 GtCO2 from 2020 onwards, which will be surpassed in 2032 at the current levels of emissions.</li><li>Some climate models of the latest generation (CMIP6) have projected very strong warming, however these models represent unlikely futures as they simulate implausibly strong reductions in shallow cloud coverage and are difficult to reconcile with historical data.</li><li>Due to decadal changes in the spatial pattern of warming (the "pattern effect"), climate sensitivity as derived from historical data is probably underestimated. Once this effect is accounted for, "observed" climate sensitivity is in better agreement with other lines of evidence.</li></ul><p><strong>Cite as:</strong></p><p>Humphrey V., Merrifield A.L., Rogelj J., Lamboll R., Olonscheck D., Mauritsen T., Ribes A. and Knutti R. 2023. Climate sensitivity, TCRE, and its role in projections. Knowledge Gains: Summary and Implication Report. The CONSTRAIN Project. DOI: <a href="https://doi.org/10.5281/zenodo.10159472">10.5281/zenodo.10159472</a>.</p>

Abstract: Climate change is the worldwide problem facing by all the countries. The main cause behind the climate change is the disturbance of ecology and natural environment. We need an attention for saving our environment by balancing our needs. Climate is the long-term average of a region’s weather events. The earth’s climate is not static. Over the billions of years of earth’s existence, it has changed many times in response to natural causes like sun spot, ice age glaciations etc. Climate change is defined as a change in the climate that may be directly or indirectly linked to human activity that modifies the global atmosphere. This shift is distinct from the natural climate variability that has been documented throughout comparable time periods. The phrase climate change represents a change in the long-term weather patterns. Climate change is not a change of weather in particular day; it is the cumulative change of long-term weather pattern i.e. changes in climate. Climate change is the measurable effect of the continual warming trend. Climate change is usually measured in major shifts in temperature, rainfall, snow and wind patterns lasting decades or more. Humans are creating climate change by burning large amounts of fossil fuels (Coal, oil, natural gas), deforestation. (When forests are cut down or burned, they can no longer store carbon is released to the atmosphere). Gradual rise in sea level, Rise in global temperature, Ocean water getting warmer, Greenland and Atlantic ice sheath are shrinking, Arctic sea ice have also thinned out, Melting of glaciers, Severity in seasons along with the intensity and frequency of climate hazards has greatly increased (floods, heavy rainfall, dry spell, cyclones etc.), Acidification of oceans, Death of corals etc. are nothing but the pure evidences of climate change. These evidence shows two kinds of impacts, that is bifurcated broadly into environmental and agricultural aspect.

Abstract: "Climate is the average state of weather events observed on earth over many years. Changes occur in climate over time with natural or antropological (human) effects. Shifts in climate due to natural factors are defined as climate variability. Natural causes of climate change include solar eruptions, changes in the earth’s orbital parameters, and volcanism. The use of carbon- containing fossil fuels, unplanned urbanization, and the steady disappearance of forested areas that act as greenhouse gas sinks are the causes of human-induced changes in the climate. The term “climate change” refers to both driven on by human activity and the change in the climate carried on by natural factors. During the latter half of the 19th century, researches on the impact of greenhouse gases on global warming provided the basis for the first studies on climate change. The studies gained momentum following the establishment of the Intergovernmental Panel on Climate Change (IPCC) in 1988, which was initiated by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). With the 1997 approval of the Kyoto Protocol and the 2015 adoption of the Paris Agreement, an international struggle against climate change has been planned. Nationally, the First Climate Council in 2022 was held in line in an effort to fight climate change and promoting green development. Institutionally, the Climate Change and Changeability Unit was established in 1991 under the Turkish State Meteorological Service (TSMS) against climate change. In 1992, the Atmospheric Conservation and Climate Change report was published. The importance of this report is that it is the first report on climate change published in Türkiye. In 2008 for the first time, a comprehensive projection analysis was conducted as a TUBITAK project with the cooperation of TSMS - ITU. In 2012, for the first time as a public institution, the TSMS runned large-scale climate projections in Türkiye. Within the scope of projection studies, 3 global climate models outputs were simulated with a regional climate model using 2 different scenarios (RCP4.5 and RCP8.5) at 20 km horizontal resolution with the dynamic downscaling method. The climate data, which form the basis of the climate projection data operated, are the data contributed to the global climate models from 2054 observation systems of TSMS located throughout Türkiye."