The influence of climate on human migration is not obvious because weather shocks can both incentivize people to migrate and reduce their ability to move. Existing empirical estimates of weather-related migration vary widely and are partly contradictory. Using data from global censuses, weather stations, and satellites, we estimate whether differences in demographic characteristics of migrants help explain migration responses to temperature and soil moisture shocks, within and across borders. We find that absent demographic information, ours and previously published models of migration fail to demonstrate an out-of-sample predictive effect of weather shocks. Predictive performance, however, improves by a factor of 6 or more when weather effects are allowed to differ according to age and education. We find that heat stress increases cross-border migration rates of highly educated older adults, but decreases rates among less educated and younger groups. Projections based on our empirical specifications suggest that omitting demographic heterogeneity leads to substantial underestimates of the magnitude of climate change effects on cross-border migration over the 21st century. Overall, our results illustrate the utility of demographic-conscious policies for addressing the nuances of climate-related migration.

Climate-driven migration figures prominently in scholarly discussions debating how climate change might threaten the international order. Whereas the mechanism typically considered involves increased conflict between states, we suggest a distinct
channel. For the international order to maintain claims to legitimacy, we show that a condition has emerged under climate change: one to protect the right to a livable space. Climate-related migration constitutes a set of circumstances in which this right becomes at risk of violation. In this context, the normative framing of livability offers two benefits. First, the livability framework reconciles the current institutional setup on climate migration with the empirical evidence. Whereas the former is primarily focused on involuntary movement across national borders, the latter documents a range of migratory responses to climate instability, from movement to immobility. By addressing such heterogeneity of outcomes, the right to a livable space overcomes limitations of prevalent normative approaches on climate mobility. Second, the livability framework helps evaluate and improve governance schemes relevant for climate mobility. Among
these, we identify the climate regime under the Paris Agreement (PA) as best suited for protecting the right to a livable space. We show, however, that a revision of the PA’s treatment of climate mobility is required to implement this right. We suggest two pathways to that end, which highlight contrasted understandings of how the PA’s two pillars of Loss & Damage and Adaptation ought to be articulated. Overall, the right to livability provides a normative foundation for a change in institutional setup of climate mobility, a defining issue for the future of the international order.

The inclusion of a 1.5◦C limit on increase of global mean temperature in the 2015 Paris Agreement has been widely acclaimed as a key achievement. Many international treaties contain similar “aspirational goals": explicit and ambitious targets with low legal obligation. Scholars have claimed that they impact policy, e.g. in regard to human rights norms. Yet few studies investigate the impact of aspirational goals contained in some of the nearly 300 international environmental agreements.
This paper identifies six general causal mechanisms through which such goals in an agreement might alter concrete policies. It then investigates their potential real-world impact using a nested case study design. Starting from an original historical dataset of all international historical environmental agreements (n=289), we find only eight that contain truly aspirational goals. Detailed case studies of these reveal two – those to mitigate acid rain in Europe and depletion of the ozone layer – where evidence suggests that aspirational goals influenced policy change. In those apparently exceptional cases, impact appears to have been contingent on the prior existence of a highly mobilized coalition. We conclude with tentative implications for the 1.5◦C target in the context of the recent attention it has received, as well as for similar aspirational goals in other issue areas.

Although migration can be an effective adaptation strategy, it requires resources. Climate change impacts can restrain such resources, thereby leading to what has been called “trapped populations.”
In this project, we build on the work described below and, additionally, incorporate within-region income distributions. We show that climate change leads to decreases in emigration of populations with lowest income levels by over 10% in 2100 for medium development and climate scenarios, and by up to 35% for more pessimistic scenarios including catastrophic damages. This suggests that the effect of climate change on resource-constrained immobility is likely to play a key role in the climate-migration nexus, leaving populations in states of extreme vulnerability. Such prospects should be of immediate and significant concern to policymakers.

Migration may be increasingly used as an adaptation strategy to reduce exposure and vulnerability to climate change impacts. Yet border policy can restrain the use of such an adaptive mechanism, with potentially dire consequences for migrants.
This project is the first to incorporate dynamic migration and remittance modeling in a leading Integrated Assessment Model. We quantify the effects of four scenarios of border policy on population distribution, income, exposure and vulnerability, CO2 emissions, and temperature for the period 2015-2100 along five scenarios of future development and climate change. We obtain three results. First, when allowed, two thirds of migrants from developing countries move to areas where they are less exposed and vulnerable to climatic risk than where they came from. Second, migration and remittances positively contribute to climate change adaptation, increasing per capita income by up to 2.6% in exposed locations. Third, restrictive border policy increases exposure and vulnerability by up to 10 percentage points of GDP by keeping people in areas where they are more exposed and vulnerable than where they would otherwise migrate. Our findings show that migration policy should be at the forefront of international climate policy deliberations.

socioeconomic and climatic variables are required as input. Consistency of migration assumptions between scenarios and models is key to avoiding partial or double counting of migration flows. For example, the Shared Socioeconomic Pathways (SSP), widely used projections of population, income, inequality, and emissions along five narratives of future development, include assumptions on international migration. But while those assumptions are explicitly quantified in their population projections, they are only implicit in the projections of other variables.
Here, we explicitly quantify the effect of international migration on income and inequality projections by comparing the original SSP quantifications to ones with zero migration. We obtain income projections without migration by removing two effects of migration on income dynamics: changes in population size and remittances. We show that migration makes the world richer in all SSP narratives. Effects of migration on income can be substantial, ranging from -5% to +21% at the continental level. We show that migration decreases income inequality across countries, does not affect within-country inequality in origin countries, and decreases it in most destination countries. In addition to informing the two modeling projects described above, these new projections ensure consistency within the SSP framework. Our scenarios are designed to be used as input in projection exercises of migration in the context of climate change, and are available in the IPCC scenarios database of the recent 6th Assessment Report.

Another key feature of the 2015 Paris Agreement are Nationally determined Contributions (NDCs), which summarize domestic objectives for greenhouse gas emission 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 greenhouse gas emissions in 2030.

In this project, we provide an analysis of uncertainty sources and their impacts on 2030 global emissions based solely on stated objectives in the NDCs. We estimate that NDCs project global emissions of 56.8-66.5 GtCO2eq yr-1 in 2030, which is higher than previous estimates and has a larger uncertainty range. Despite these uncertainties, NDCs robustly shift emissions towards emerging and developing countries and reduce international inequalities in per capita emissions. Finally, we stress that current NDCs imply larger emission 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: 1) a clearer framework regarding future NDC design, 2) an increasing participation of emerging and developing countries in the global mitigation effort, 3) an ambitious update mechanism to avoid unrealistic decarbonization rates after 2030, and 4) an anticipation of steep decreases in global emissions after 2030.