Climate change can both incentivize people to migrate and reduce their ability to move, making its effects on human migration theoretically ambiguous. Using data from global censuses, weather stations, and satellites, we analyze migration within and across borders in relation to weather and migrant demographics. Allowing historical weather effects to differ by age and education improves out-of-sample performance by a factor of four or more compared with a homogeneous effect. For example, heat and dryness increase cross-border migration of less educated older adults but decrease migration among younger groups, while highly educated individuals are little affected. Accounting for demographic heterogeneity reveals projected effects of climate change on migration that are an order of magnitude larger for most demographic groups, with responses of different groups offsetting one another.

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 pledge to limit the increase in global mean temperature to 1.5°C has been widely acclaimed as a key achievement of the 2015 Paris Agreement. Many international treaties contain similarly explicit and ambitious “international aspirational goals” (IAGs) with low legal obligation. While an extensive literature claims such goals impact policy in areas like human rights and development, few studies investigate the impact of IAGs contained in international environmental agreements. Starting from an original historical dataset of all international historical environmental agreements (nearly 700), this paper identifies six general causal mechanisms through which such IAGs might alter concrete policies, then uses a nested case study design to estimate their real-world impact. Of the eight regime complexes including 80 treaties with IAGs, we find just two – mitigation of acid rain in Europe and depletion of the ozone layer – where they could possibly have influenced policy change. Even in those exceptional cases, their impact appears to be limited largely to encouraging or marginally enlarging an already highly mobilized coalition of “like-minded” states. These conclusions counsel data-based skepticism regarding the transformative potential of the 1.5°C climate target and other similar treaty-based ideals in international life.

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.