Mechanisms of Climate Change

The current emissions of Greenhouse gases (GHGs) are causing massive changes in atmospheric and ocean dynamics, by trapping heat that otherwise would be radiated into space. Because of this, the overall energy balance of storing solar energy during warm seasons and radiating energy to space during winter is broken, today we are storing more and more energy than what is radiated out of the planet (Figure 1). In addition, part of the atmospheric temperature excess is transferred to the ocean, which functions as a heat reservoir, disrupting in turn, the ocean-atmosphere heat exchange balance. Ocean heat and warmer days are causing glacial melting in the poles with a subsequent sea-level rise. Glaciers on high mountain ranges are also melting, affecting river flow (EPA, 2022).

Figure 1. Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrous oxide, absorb heat energy and emit it in all directions (including back to the planet), keeping Earth’s surface and lower atmosphere warm. Adding more greenhouse gases to the atmosphere enhances trapping more heat, and consequently, Earth’s surface and lower atmosphere are even warmer. Source: US EPA.

Excess energy is causing an increase in the frequency and intensity of extreme events, as systems tend to dissipate surplus energy to restore their overall balance. Warm oceans, moist warm air, and light upper-level winds are key ingredients for the formation of hurricanes and tropical storms. These originally functioned as a mechanism to restore balance as they remove heat from the ocean in the form of moisture which pumps the heat up into the atmosphere, and ideally, this heat would be radiated out into space. But now pumping heat into the atmosphere just increases overall air temperature as heat is trapped in the atmosphere due to GHGs (Figure 2). Changes in precipitation patterns – either heavy rains causing flooding or lack of rain for extended periods causing droughts – are the result of a more complex interplay between global warming, deforestation and land use change, soil erosion, change in river courses and extractive practices of underground water, to name the most important (EPA, 2022, RS, 2022).

Figure 2. Global temperature change over the last 2019 years, reconstructed from several proxy records, like tree rings, cave deposits, corals, etc., showing the current upward trend in temperature over the last 60 years. Source: Hawkins, 2020.

The most recent report of the State of the Global Climate 2021 and the IPCC 6^th report show with medium to high confidence that all Global Climate Indicators (greenhouse gases, global temperature, ocean acidification, sea level rise, glacial and ice melting, Antarctic ozone hole and weather variability) are continuing to rise, induced by human activities, with no signs of slowing down (WMO 2021, IPCC 6^th Assessment, 2022a). This in turn creates the extreme events that we all have been witnessing in recent years with heat waves, droughts, heavy storms producing flooding and extensive forest fires (WMO No. 1290, 2022, IPCC 6^th Assessment, 2022b).

However, an holistic approach is needed as our planet is not only going through Climate Change driven by GHGs but also through biodiversity loss, heavy pollution, and diminished ecological functions, which in turn drastically reduce Earth’s natural capacity to buffer changes (EU, 2009, IPCC, 6^th Assessment, 2022b), causing the system to potentially cross several tipping points (Figure 3), which would drastically modify Earth’s atmospheric and ecological dynamics, creating a clear emergency as this leads to a new, less habitable, ‘hothouse’ climate state (Lenton, 2008).

Figure 3. Map showing the key tipping points at a global scale. Source: PIK, based on Armstrong McKay et al., Science (2022)

To slow global change, a multisectoral approach is needed, where sectors driving emissions need to change their energy source and energy efficiency (Figure 4). Additionally, a set of concerted actions regarding ecosystem conservation and restoration, nature-based solutions, change in consumption patterns, sustainable development, and social equity need to be implemented at the same time and on a large scale.

These actions need to be promoted both by top-down and bottom-up initiatives. There is enough information, initiatives and ideas to help the world to transition to a state that allows a flourishing future for all life on this planet – including the 9 to 11 billion people projected for the near future – but they need to be supported by the right policies and funding (Figure 5) (IPCC 6th Assessment, 2022b).

Figure 4. Pie-chart showing Greenhouse Gas emissions by sector in 2020. Source: Our World in Data.

Figure 5. Interactions among the coupled systems: climate, ecosystems (including their biodiversity) and human society. These interactions are the basis of emerging risks from climate change, ecosystem degradation and biodiversity loss and, at the same time, offer opportunities for the future. Source: IPCC 6^th Assessment, 2022b.

Figure 5 displays the coupling between different components of the climate system. (a) Human society causes climate change. Climate change, through hazards, exposure and vulnerability generates impacts and risks that can surpass limits to adaptation and result in losses and damages. Human society can adapt to, maladapt and mitigate climate change, ecosystems can adapt and mitigate within limits. Ecosystems and their biodiversity provision livelihoods and ecosystem services. Human society impacts ecosystems and can restore and conserve them. (b) Meeting the objectives of climate resilient development thereby supporting human, ecosystem and planetary health, as well as human well-being, requires society and ecosystems to move over (transition) to a more resilient state. The recognition of climate risks can strengthen adaptation and mitigation actions and transitions that reduce risks. Taking action is enabled by governance, finance, knowledge and capacity building, technology and catalysing conditions. Transformation entails system transitions strengthening the resilience of ecosystems and society (Section D). In a) arrow colours represent principle human society interactions (blue), ecosystem (including biodiversity) interactions (green) and the impacts of climate change and human activities, including losses and damages, under continued climate change (red). In b) arrow colours represent human system interactions (blue), ecosystem (including biodiversity) interactions (green) and reduced impacts from climate change and human activities (grey).

Mechanisms of Climate Change

References