Lecture 8 — Projections and Consequences of Inaction

Part 1 (20 Minutes): Overview and Illustrative Explanation

In this section I outline the basic developments to be expected if global emissions are not effectively reduced. The description is based on the latest comprehensive assessments of the Intergovernmental Panel on Climate Change (IPCC) and complementary analyses by international organizations. It is important to note in advance: the following statements summarize the scientific consensus, but also indicate areas of uncertainty, for example regarding long-term feedbacks and local projection details (see references at the end).

Imagine the Earth as a house with an interior temperature that is slowly rising. As long as the heating runs moderately, one can maintain comfort by ventilating and local measures. But if the heating runs increasingly stronger, windows, furniture and the structure of the house will be permanently damaged. Analogously, "inaction" on climate protection means: the drivers of warming — mainly greenhouse gas emissions — remain high, the global mean temperature continues to rise, and stresses on people, nature and infrastructure increase both in intensity and frequency. This development is not linear: small additional warmings can lead to significantly larger damages because multiple processes interact.

Scientific projections use standardized emissions pathways ("SSP" scenarios) and climate models to generate possible future images. Without substantial emissions reductions, scenarios with persistently high emissions are possible, which can have very severe long-term consequences. Observable and model-confirmed impacts include a higher frequency and intensity of heatwaves, stronger precipitation events in some regions, increasing droughts in other areas, accelerated sea level rise, and negative impacts on agriculture, health and ecosystem services (IPCC AR6 Summary; IPCC WGII).

Regional differences are crucial: densely populated coastal regions are particularly vulnerable to sea level rise, Sahel zones and Mediterranean rim countries face increased drought risks, while tropical regions experience stronger heat-related health risks and crop losses. Some island states and low-lying coastal areas face existential risks because land areas and freshwater resources can be lost (IPCC WGII; NASA Sea Level).

Also important is the effect on ecosystems: biodiversity losses, shifts in habitats and the possibility of irreversible damage to coral reefs, wetlands and polar systems are documented. These losses affect not only nature itself but also the services on which people depend — for example fisheries, pollination and water regulation (IPBES; IPCC WGII).

Part 2 (20 Minutes): Technical Terms, Scenarios, Tipping Points and Costs

Key Terms and the Structure of Projections

International climate projections use standardized emissions pathways known as Shared Socioeconomic Pathways (SSPs). These pathways combine socioeconomic developments with different emissions trajectories; they are fed into climate models that represent physical processes. The IPCC reports integrate results from many models to provide a picture of possible climate developments (IPCC AR6 WGI, IPCC AR6 Synthesis).

Tipping Points and Nonlinear Risks

A central concept is so-called "tipping points" or "tipping elements" — components of the Earth system that can flip into a new state after certain thresholds are crossed. Classic examples are the large-scale loss of ice mass in Greenland or the West Antarctic, substantial changes in tropical coral ecosystems, or a strong weakening of the Atlantic Meridional Overturning Circulation (AMOC). These processes can involve very long timescales and are associated with large uncertainties: the probability of a flip and the exact threshold location are subjects of active research; nevertheless these risks are considered plausible and potentially irreversible on human timescales (Lenton et al. 2008; IPCC AR6 WGI).

Regional and Sectoral Impacts — A Closer Look

Climate impacts are sector- and region-specific. The IPCC work distinguishes direct physical risks (e.g., heat, storm surges), indirect risks (e.g., yield declines due to changed water availability) and systemic risks that arise from interactions between sectors and regions (such as supply disruptions following extreme events). Health impacts include heat-related deaths, the spread of vector-borne diseases into new areas and burdens from deteriorating air quality. Agricultural yields respond heterogeneously: in cool regions moderate warming can temporarily increase productivity, whereas in many tropical and mid-latitude regions yield declines occur with increasing warming (IPCC WGII).

Economic Costs of Inaction — Approaches and Findings

The question of the costs of doing nothing is answered from different perspectives: direct damages to infrastructure, indirect economic effects (e.g., disrupted supply chains), health costs and long-term losses of welfare. Large syntheses and model calculations consistently conclude that unlimited "business as usual" leads to high aggregate economic damages and that these damages accumulate over time. There are significant uncertainties in the quantitative magnitude, but it should be made clear that several international assessments — including IPCC work and World Bank reports — warn of serious consequences for economic growth and poverty outcomes if adaptation measures and emissions reductions are lacking (IPCC AR6 WGII; World Bank Shock Waves; UNEP Emissions Gap Report 2023).

Limits to Adaptation and Residual Damages

Another important term is the "limit to adaptation": for some impacts there are physical or economic limits beyond which adaptation is no longer possible or only feasible at disproportionately high cost. Examples are the permanent disappearance of island areas, the die-off of large-scale coral reefs, or irreversible species losses. The IPCC reports point out that even with extensive adaptation residual damages will remain, especially at higher levels of warming (IPCC AR6 WGII; GCA Adapt Now).

Uncertainties and Research Gaps

Scientific uncertainties mainly concern the spatial resolution of regional projections, the quantification of feedbacks (such as permafrost carbon release), the timing and probability of tipping points, and the socioeconomic dynamics that drive emissions. These gaps affect exact cost estimates and precise timing for particular damages; however, they do not diminish the qualitative conclusion that inaction significantly increases risks (IPCC AR6 Synthesis; Lenton et al. 2008).

Part 3 (10 Minutes): Applications, Limits and Thought Exercises

Concrete application: planners in coastal cities must now incorporate expectations of sea level rise into their infrastructure planning — roads, sewer systems and port facilities have long lifecycles. Data and projections on local sea level rise (e.g., compiled by NASA and the WMO) are essential for decisions; the scientific uncertainty does not mean that no robust options exist, but it does mean that flexible and iterative strategies (so-called adaptive pathways) are sensible (NASA Sea Level; WMO Statement).

Limits of projections: climate models provide robust signals at the global level, while reliability of projections decreases at local scales, particularly for precipitation changes. Therefore, a pragmatic approach to uncertainty is necessary in decision-making: one should prioritize measures that provide benefits under both moderate and strong warming — so-called "no-regret" measures — while also planning based on scenarios (IPCC AR6 WGI; IPCC AR6 Synthesis).

Small thought exercises for deeper consideration (please work through mentally): 1) Assume your municipality expects more frequent extreme precipitation in 30 years. Which types of infrastructure would you examine first and why? 2) Imagine average temperatures in your region rise so much that traditional crops increasingly suffer yield losses. What short-term and what long-term adaptation options would be conceivable, and what might be the limit of this adaptation? 3) Consider which economic actors — insurers, supply chain firms, municipal administrations — would be most affected by continued inaction and how they might respond.

In conclusion: the scientific evidence clearly shows: inaction increases risks, exacerbates inequalities between regions and can cause irreversible damages. There are uncertainties in details and in the quantification of costs, but the direction and nature of the threats are well documented. The literature also offers practical routes to more resilient planning that account for uncertainties and combine short-term measures with a long-term perspective (IPCC AR6 Synthesis; UNEP Emissions Gap Report 2023; GCA Adapt Now).