December 2, 2019，The 25th Conference of the Parties to the United Nations Framework Convention on bet365 offers Change opens in Madrid, the capital of Spain，Due to differences on key issues，The meeting was postponed for two days and closed，All parties failed to reach consensus on core issues。With the increasingly serious situation of global warming，bet365 offers change issues are increasingly attracting academic attention，On the one hand, it reflects the urgency and importance of this issue，On the other hand, it reflects the country、Government、Enterprises and other departments have a growing demand for relevant research on scientific assessment of bet365 offers impacts and basis for decision-making。Since mitigation and adaptation are the main responses to global bet365 offers change，Academic research surrounding these two aspects is also the most concentrated。For the former，Involving emission reduction path analysis、Emission reduction cost assessment、Emission reduction policy design、Emission reduction technology selection, etc.；The latter includes adaptation cost analysis、Adaptation effect assessment、Adaptation measure selection，And analysis of the interactive effects of adaptation and emission reduction, etc.。

It is worth mentioning，Most climate economic research and comprehensive policy assessment work are based on Integrated Assessment，IA) bet365 offers。This type of bet365 offers describes the economy、Unique advantages in the complex dynamic interactions between systems such as energy and climate，These relationships often play a decisive role in future climate change and effective climate policy choices。The comprehensive assessment bet365 offers was first born in the 1970s，The Dynamic Integrated Climate Economic bet365 offers (DICE) developed by Professor William Nordhaus of Yale University is the most outstanding representative。Although early IA models considered the interaction between economy and climate，But only carbon dioxide (CO2) concentration and average temperature change are selected as environmental variables，And only carbon emissions related to human activities are considered，The bet365 offers was then gradually expanded to include the earth’s carbon cycle、Land use carbon emissions、Non-carbon emissions, local air pollutant emissions and other multi-dimensional environmental variables and greenhouse gas (GHGs) emissions，At the same time, the feedback mechanism of climate change on the economic system is fully considered。Overview of the development of IA bet365 offers，It can be said to be derived from economics，Experience the Earth、Integrated development of climate and environmental systems，Finally back to the study of economic issues。

Different IA models are divided into regions、Start year selection、There are large differences in simulation time span and other aspects。For example，Models such as DICE and E3METL are typical global single-region single-sector models，And RICE and WITCH have expanded to multi-regional scale。In addition，Even from a global single-sector bet365 offers，Future economic growth expectations of each IA bet365 offers、Population growth、Energy technology progress、Technology Portfolio、Assumptions on many aspects such as mitigation or adaptation policy options are also inconsistent。Take economic growth expectations as an example，The DICE bet365 offers is the most optimistic about future economic growth expectations，Followed by RICE and E3METL models，The WITCH bet365 offers is relatively pessimistic about the future global economic situation。This also explains to a large extent why the research results of different models on the same policy issue are significantly different。As far as the optimal carbon tax path (or social carbon cost SCC) is concerned，Under the 2℃ temperature control target，GCAM bet365 offers、The simulation results of the DICE bet365 offers and the WITCH bet365 offers both show that the endogenous carbon tax path is monotonically increasing，And the optimal carbon tax level in the GCAM bet365 offers at the end of the 22nd century is about 310 US dollars/ton of carbon，This result is closer to the WITCH bet365 offers，But only 1/3 of the corresponding DICE bet365 offers results。

Then，How to ensure the stability of different IA bet365 offers results，Especially draw conclusions from which the differences are small or relatively consistent，It is particularly important to support decision-making more scientifically and reliably，This actually brings challenges to the current climate economic modeling theory。In this context，bet365 offers comparison methods based on different IA frameworks emerged at the historic moment。Especially in the past 5 years，bet365 offers comparison research has gradually become a new trend in climate policy research。Although European and American countries established the “Exchange bet365 offers Differences” as early as 1979,，Energy Modeling Forum (EMF), the official forum for improving government decision-making，But until around 2010，Related research based on bet365 offers comparison methods has gradually emerged and become a hot topic to solve the problem of policy research stability。Subsequently，Many projects and related conclusions based on bet365 offers comparisons were included in the IPCC Fifth Comprehensive Assessment Report and 1.Special report on 5℃。Driven by the need for policy stability and decision-making，In recent years，Multi-bet365 offers comparative analysis method has gradually become the academic field to assess global and regional climate change risks、Hot methods for climate-related issues such as emission reduction and adaptation mechanism design。

Currently，Theoretical development and empirical research on multi-bet365 offers comparison at the global level have achieved a series of innovative results，And obtained many consistent findings。First，Achieving the 2°C temperature control target requires all countries around the world to fully participate and effectively reduce emissions，Compared to the case of partial participation，The cost of achieving the established goals has been significantly reduced。Secondly，Carbon Direct Air Removal (CDR), which is not optimistic if current feasibility is not considered、Negative emission technologies such as biomass carbon capture and storage (BECCS)，Starting from now on to effectively reduce emissions as early as possible is the safest choice to achieve this goal。Again，Wind energy、Key renewable energy technologies such as solar energy，And the vigorous development of CCS technology will be a feasible technical guarantee to achieve the 2℃ temperature control goal。Finally，The intensity of the nationally determined contributions (NDCs) committed by countries in the Paris Agreement is far from sufficient to support the achievement of the 2°C temperature control goal，Therefore，The policy cost to achieve the NDC target is also far lower than the temperature control threshold target。

In fact，The significance of the development of multi-bet365 offers comparative analysis methods is far beyond policy design，It is of great significance to the improvement of comprehensive assessment modeling methods and even the entire climate economic theory。Through bet365 offers comparison and analysis，Helps us find sources of uncertainty in results，Better policy simulation with modified models。Generally speaking，bet365 offers structure (top-down or bottom-up)，Valuation of key parameters (production factor input elasticity、Technological substitution elasticity, etc.)，For future economic growth、Population growth、Expected assumptions for energy demand, etc.，Technical selection and feasibility settings，Time preference rate and discount rate selection, etc.，is the main source of uncertainty currently causing uncertainty in IA bet365 offers policy simulation and evaluation results。

Since 2010，The academic community’s emphasis on multi-bet365 offers comparative analysis methods has significantly improved，But the number of relevant studies is still small，Obviously does not match the research needs of climate change issues。On the one hand，Current research focuses on the analysis of emission reduction paths under established climate goals、Policy Cost Assessment、Energy technology development、Limited aspects such as the relationship between climate policy and energy security，And the carbon market、Energy Tax、The impact of representative climate policies such as renewable energy subsidies (FIT) on emission pathways、The impact of technological substitution evolution，Economy in the process of achieving climate goals、Technology、The role of multiple uncertainties such as climate sensitivity，The reduction and control effect of climate adaptation on climate loss risks，There is a lack of research support on a series of key climate-related issues such as the dynamic interaction between emission reduction and adaptation。On the other hand，Current multi-bet365 offers comparative research is mostly focused on the global scale，But in fact，The regional characteristics of climate change issues are also very significant。This is not only reflected in regional differences in GHGs emissions and climate change impacts，More importantly，Global greenhouse gas emission reduction tasks need to be implemented in specific countries or regions。Therefore，From the regional level，Especially for China、United States、It is of great significance to conduct multi-bet365 offers comparative studies on climate policy issues in economies such as India。

Statistical results display of multi-bet365 offers comparative studies，The current IA bet365 offers research is mainly led by Europe and the United States，These models include both top-down and economically oriented models，There are also bottom-up technology-driven models，But the common features are significant advantages in considering GHGs emission control policies and energy technology substitution policies。Judging from the geographical distribution of the bet365 offers，Most of the currently most widely used primary models are distributed in Europe and the United States，Europe is dominated by the Netherlands and Germany。This is because the two countries have famous climate change research institutions，The Potsdam Center for Climate Change Research (PIK) in Germany、Energy Research Center Netherlands (ECN) and Netherlands Environmental Assessment Agency (PBL)。And other countries or regions except Japan，The primary bet365 offers research capabilities of China and India, the major emitters, are both weak。

Can be expected，bet365 offers comparison research methods will play a more important role in future climate change research。According to the IPCC Sixth Comprehensive Assessment Report，Emission path analysis of national level budget constraints、Stable emission reduction policy design has created a greater demand for bet365 offers comparison research。Of course，Further strengthening climate economic research across models requires focused consideration of some key issues。One，Each country vigorously develops a bet365 offers based on its specific national conditions，Especially in developing countries with high emissions such as China and India，Is the most important prerequisite for future multi-bet365 offers comparative research work in these countries，It is also a key link in improving the regional climate economic theory。Although the current multi-regional models developed by Europe and the United States and other countries often list major emitters separately，But the basis of modeling (data and parameter estimation reliability，To the economy、Prediction of energy consumption trends, etc.) is far less solid than the bet365 offers for the country。Part 2，Create effective cross-country/region、Cross-team research collaboration，This is the basis for building a multi-bet365 offers comparative research framework。On the one hand, specific research questions need to be addressed，In particular, multiple parties reached a consensus on the importance of the issue，On the other hand, some good incentive mechanisms need to be designed to increase the enthusiasm of multiple parties to participate。Part 3，Make a reasonable selection of qualified models，To better support research on real-life problems。In fact，In addition to the wishes of the bet365 offers team，Whether the bet365 offers itself is suitable for the research of specific problems is also very critical。For example，bet365 offers structure problem、Micro-level data availability issues、Solving feasibility issues, etc.，All are important considerations in bet365 offers selection。

　(Author’s affiliation: School of bet365 offers and Management, University of Chinese Academy of Sciences)