Understanding the impact of climate change on human migration is critical for policymakers. Yet climate change can both incentivize people to migrate and reduce their ability to move, making its effect on human migration theoretically ambiguous. We propose a new approach that combines causal inference methods with cross-validation techniques to reliably estimate effects of weather on migration within and across borders. This approach highlights the key role of migrant demographics in the weather-migration relationship. We show that allowing weather effects to differ by age and education improves out-of-sample performance by a factor of five or more compared with a homogeneous effect. Demographic heterogeneity is critical in explaining this discrepancy. Projections based on our empirical estimates indicate that the effects of climate change on future cross-border migration will be an order of magnitude larger for most demographics than the average effect, but responses of different groups largely offset one another.

Globally, populations are increasingly located in areas at high risk of climate change impacts. Some populations lack the agency to move out of harm’s way, leading to involuntary immobility. The climate risks these populations face are insufficiently addressed in climate policy and disaster planning. While policy and planning should be data-informed, the lack of appropriate data should not limit governments and institutions from taking action to reduce the risk of involuntary immobility. Incorporating involuntary immobility within the broader sustainable development goals of climate action and safe, orderly, and regular migration may substantially reduce the risk of involuntary immobility.

Migration is a widely used adaptation strategy to climate change impacts. Yet resource constraints caused by such impacts may limit the ability to migrate, thereby leading to immobility. Here we provide a quantitative, global analysis of reduced international mobility due to resource deprivation caused by climate change. We incorporate both migration dynamics and within-region income distributions in an integrated assessment model. We show that climate change induces decreases in emigration of lowest-income levels by over 10% in 2100 for medium development and climate scenarios compared with no climate change and by up to 35% for more pessimistic scenarios including catastrophic damages. This effect would leave resource-constrained populations extremely vulnerable to both subsequent climate change impacts and increased poverty.

The Shared Socioeconomic Pathways (SSPs) represent five narratives of future development used for climate change research. They include quantified projections of socioeconomic variables such as population, income levels, inequalities, and emissions over the twenty-first century. The SSP’s population projections embody explicit, pathway-specific international migration assumptions, which are only implicit in the projections of other variables. In this contribution, we explicitly quantify the effects of international migration on income levels and income inequality across and within countries by comparing the original SSP projections to scenarios of zero migration. Income projections without migration are obtained by removing two effects of migration on income dynamics: changes in population size and remittances sent to origin countries. We base our remittance estimates on migrant stocks derived from bilateral migration flow estimates obtained from a gravity model. We find that, on average, migration tends to make the world richer in all SSP narratives. The nature of migration and remittance corridors is shaped by the specific scenario of future development considered. Depending on the particular SSP narrative and world region considered, the effects of migration on income can be substantial, ranging from −5 to +21% at the continental level. We show that migration tends to decrease income inequality across countries and within country in most destination countries but does not affect within-country inequality in origin countries. This new set of projections is consistent with the interdisciplinary framework of the SSPs, which makes it particularly useful for assessing global climate and sustainable development policy options.

Migration may be increasingly used as adaptation strategy to reduce populations’ exposure and vulnerability to climate change impacts. Conversely, either through lack of information about risks at destinations or as outcome of balancing those risks, people might move to locations where they are more exposed to climatic risk than at their origin locations. Climate damages, whose quantification informs understanding of societal exposure and vulnerability, are typically computed by integrated assessment models (IAMs). Yet migration is hardly included in commonly used IAMs. In this paper, we investigate how border policy, a key influence on international migration flows, affects exposure and vulnerability to climate change impacts. To this aim, we include international migration and remittance dynamics explicitly in a widely used IAM employing a gravity model and compare four scenarios of border policy. We then quantify effects of border policy on population distribution, income, exposure, and vulnerability and of CO 2 emissions and temperature increase for the period 2015 to 2100 along five scenarios of future development and climate change. We find that most migrants tend to move to areas where they are less exposed and vulnerable than where they came from. Our results confirm that migration and remittances can positively contribute to climate change adaptation. Crucially, our findings imply that restrictive border policy can increase exposure and vulnerability, by trapping people in areas where they are more exposed and vulnerable than where they would otherwise migrate. These results suggest that the consequences of migration policy should play a greater part in deliberations about international climate policy.

Nationally Determined Contributions (NDCs), submitted by Parties to the United Nations Framework Convention on Climate Change before and after the 21st Conference of Parties, summarize domestic objectives for greenhouse gas (GHG) emissions reductions for the 2025–2030 time horizon. In the absence, for now, of detailed guidelines for the format of NDCs, ancillary data are needed to interpret some NDCs and project GHG emissions in 2030. Here, we provide an analysis of uncertainty sources and their impacts on 2030 global GHG emissions based on the sole and full achievement of the NDCs. We estimate that NDCs project into 56.8–66.5 Gt CO2eq yr−1 emissions in 2030 (90% confidence interval), which is higher than previous estimates, and with a larger uncertainty range. Despite these uncertainties, NDCs robustly shift GHG emissions towards emerging and developing countries and reduce international inequalities in per capita GHG emissions. Finally, we stress that current NDCs imply larger emissions reduction rates after 2030 than during the 2010–2030 period if long-term temperature goals are to be fulfilled. Our results highlight four requirements for the forthcoming 'climate regime': a clearer framework regarding future NDCs' design, an increasing participation of emerging and developing countries in the global mitigation effort, an ambitious update mechanism in order to avoid hardly feasible decarbonization rates after 2030 and an anticipation of steep decreases in global emissions after 2030.

At each Conference of Parties (COP), scientists hand over the climate change problem to diplomats and policymakers. A COP also offers scientists a chance to take stock of their research, confront emerging policy questions, identify research gaps, and update their research agendas. We, as an interdisciplinary group of academic experts who have been providing independent insights to the COP21 French presidency and negotiation team (1), have seen not only the importance of science in policymaking but also its limitations and sometimes its lack of alignment with the complex environmental and societal issues addressed in the negotiations. Here we analyze research gaps and identify new directions of research in relation to a number of facets of the Paris Agreement, including the new 1.5 °C objective, the articulation between near-term and long-term mitigation pathways, negative emissions, verification, climate finance, non-Parties stakeholders, and adaptation.

A pledge to limit global warming “to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C” has been widely acclaimed as the key achievement of the 2015 Paris Agreement. Other international agreements contain similarly explicit, ambitious but non-binding international aspirational goals (IAGs). Extensive literature claims IAGs impact policy in areas like human rights and development, yet no study investigates the impact of IAGs on international environmental cooperation. Starting from a new historical dataset of 696 international environmental agreements across 73 issues, we identify six general causal mechanisms through which IAGs might alter concrete policies, then estimate their real-world impact. Of the eight regime complexes including 80 agreements with IAGs, we find just two – mitigation of acid rain in Europe and depletion of the ozone layer – where IAGs could possibly have influenced policy change. Even in these exceptional cases, the impact appears limited: at most, IAGs slightly encourage or marginally enlarge an already mobilized coalition of “like-minded” states. Throughout, wealth, abatement costs, domestic political support, and relative power explain more concrete policy change. These conclusions counsel data-based skepticism about the potential for the 1.5/2°C climate target and other agreement-based international aspirational goals to drive concrete policy change.

Climate-driven migration figures prominently in discussions debating how climate change might generate global instability. Accordingly, current institutions mainly address cross-border displacement. However, empirical evidence documents a broader range of responses to climate instability, from movement to immobility. We propose a normative framework for governing climate mobility that addresses this mismatch, based on the right to a livable space. Climate-related migration constitutes a set of circumstances in which this right becomes at risk. We highlight this right’s origin, scope, and who is responsible for protecting it. Framing climate mobility through livability offers two benefits. First, it helps address the full range of mobility outcomes, thereby overcoming limitations of prevalent normative approaches. Second, it helps evaluate relevant governance schemes. We examine the Paris Agreement as a potential institution for implementing this right. Overall, livability offers a normative foundation for rethinking climate mobility governance, an issue linking two major challenges for interstate relations.

Since the Syrian civil war, possible climate-migration-conflict interactions have attracted increasing attention. However, evidence of these links remains weak and mixed, partly because climate impacts on migration are often indirect, context dependent and difficult to quantify. Here, we assess the climate‒migration relationship through environmental and non-environmental (economic, political, demographic, and social) drivers and the potential conflict implications thereof at destinations. We apply an expert assessment, engaging 18 experts who represent a range of relevant knowledge, disciplines, and methodologies. The findings suggest that climate events, including extreme weather events and slow-onset processes, primarily drive migration and, less frequently, result in immobility. These impacts are largely mediated by non-environmental drivers, predominantly economic drivers, and act directly through environmental drivers only rarely. As global warming progresses, climate impacts on migration and immobility are expected to intensify, with economic, political (including conflict), and environmental drivers becoming more influential. To date, climate-related migration has rarely affected armed conflict at destinations, with increases outnumbering decreases. These impacts are highly context dependent, with greater conflict risk manifesting especially in areas with preexisting vulnerabilities, such as scarce resources, weak institutions, and social marginalization. Sub-Saharan Africa, South Asia, Southeast Asia, and the MENA region are judged most at risk.