While the scientific community has produced increasingly reliable knowledge about the physical consequences of global warming on time scales of tens of decades and longer,, The social and humanitarian impacts of exceeding the climate target remain largely unknown.. We are now rapidly approaching the aspirational goal of the Paris Agreement of limiting the increase in global average temperature (GMT) to 1.5°C. However, the current trajectory, based on current Nationally Determined Contributions (NDCs), suggests that we will significantly exceed this threshold before 2050.

If all unconditional and conditional NDCs were fully implemented, this could lead to a warming of up to 2.6°C GMT. This significantly increases the likelihood of a period, likely lasting a decade or more, during which significant overshoot, which is the phase where warming exceeds the 1.5°C threshold before potentially falling below it.

Five critical factors influencing impacts

The lack of evidence-based knowledge makes decision-making in crisis management and humanitarian assistance difficult. To better prepare policymakers and planners for the impacts of an exceedance, it is proposed to focus on five key areas:

1. Peak warming and duration of exceedance: The extent and magnitude of the impacts depend on how long the exceedance lasts. Even if temperatures later return below the threshold, some impacts, such as sea level rise, can no longer be reversed.
2. Geographical distribution of impacts: The impacts of exceedances will not be evenly distributed in space, time or intensity. Regions such as the Arctic and Western and Southern Africa are warming faster than the global average (regional amplification), often overlapping enhanced warming with high social vulnerability.
3. Level of exposure and vulnerability: Exposure and vulnerability will evolve non-linearly over this period.
4. Adaptation limits: Adaptation will increasingly be overstepped, leading to significant and widespread losses and damages. The cascading nature of risks exacerbates the situation.
5. Turnaround dynamics: Post-peak behavior is of fundamental, yet currently underestimated, importance for assessing human and social impacts.

A complicated road to recovery

Reversing global mean temperature (GMT) will require negative emissions and increased deployment of carbon dioxide removal (CDR) technologies. Land-based CDR methods, such as afforestation, will create significant additional demand for land, which may lead to conflict with food production and other land uses.

Recovery from the exceedance is likely to consist of varying timescales with GMT increases and decreases, as well as periods of stagnation. While some sectors may be resilient to shorter-term changes, the humanitarian sector would be less able to mitigate shifts in impacts that might occur during, for example, a 5-year period of temperature increase within a longer 30-year recovery period. These oscillations would have unique operational implications for humanitarian operations and disaster management.

Call to action

Given the extremely high stakes, it is essential to advance knowledge and action regarding the impacts of overshooting.

• For scientists: Research into the potential human and social impacts, with regard to different post-peak behaviours, needs to be accelerated and expanded.
• For humanitarian organizations: It is a responsibility to accelerate strategic planning that considers the future with varying impact developments. Future disasters will bring new stressors and shocks that may reach a level of complexity in logistics and operations that is impractical or impossible.
• For governments: There is a growing need to strengthen NDCs to ensure a realistic path back to 1.5°C GMT in ways that do not cause additional humanitarian needs and unforeseen impacts.

Increasing our understanding of how social and economic systems will be affected in the event of a exceedance is crucial for identifying and implementing appropriate adaptation and risk reduction strategies in the coming years and decades. We must focus on allocating resources to develop the knowledge and evidence needed to effectively prepare for and respond to the social impacts of a exceedance. JRi

The study was published in the journal PNAS