Climate change

What is at stake?

Catastrophic climate change has been associated with an increase in global average temperature of >3 °C. This level of global warming would probably imply a serious shift in global climate patterns, unprecedented loss of landmass creating large flows of climate refugees, significant risks to regional and global food security, a combination of high temperature and humidity jeopardising normal human activities, as well as massive species extinctions having adverse cascading effects on ecosystem functioning and services critical for sustaining humanity.

Catastrophic climate change would be triggered by crossing one or more tipping points of the Earth’s climate system. Decision-makers have tended to assume that tipping points are of low probability and poorly understood. This is in spite of growing evidence that these tipping points may be more likely than previously thought, have high impacts and interact in complex and dangerous ways, threatening long- term irreversible changes. Political discussions about climate change rarely acknowledge catastrophic climate risk.

How much do we know?

The Earth's climate is impacted by the concentration of certain gases in the atmosphere known as greenhouse gases, the most important being carbon dioxide and methane. As a result of human activity since the Industrial Revolution, the atmospheric concentrations of greenhouse gases – generally expressed as the number of greenhouse gas molecules per million or ppm – have risen consistently, from 280 ppm at the dawn of the Industrial Revolution to 407 ppm in 2018. Current carbon dioxide levels are the highest in at least 800,000 years.

Climate change is accelerating and its impacts increasing. Human actions are estimated to be causing the planet’s climate to change 170 times faster than natural forces. 2015-2019 and 2010-2019 were the warmest five and ten-year periods on record. Over the past decade, extreme weather, ice loss, sea level rise and ocean heat and acidification have accelerated.

Human activities have caused approximately 1.0 °C of global warming above pre-industrial levels. Under current policies, global temperatures are expected to exceed 1.5 °C around 2035, 2 °C around 2053 and 3.2 °C by 2100. If countries fully achieve the emissions cuts they have committed to under the Paris Climate Agreement, the planet is likely to warm by approximately 2.9 °C by the end of the century. Most of the world’s major emitters are not even on track to meet their pledges.

Climate change is a non-linear phenomenon where tipping points play a determining role. When warming rises above a certain level, self-reinforcing feedback loops set in and the concentration of greenhouse gases increases rapidly. Although precise thresholds and exact scenarios remain very uncertain, we know that the level of risk increases with the rise in temperature. The latest science suggests that tipping points could be exceeded even between 1.5°C and 2°C. For example, at 2 °C of warming there is a 10-35% chance that the Arctic becomes largely ice-free in summer.

"There is a serious risk that political and public attention to climate issues will dramatically decline in the face of the pressing, severe economic and social consequences of the crisis."

Scientists recently found that 45 per cent of all potential ecological collapses are interrelated  and could reinforce one another; in other words, ‘exceeding tipping points in one system can increase the risk of crossing them in others'.

 Limiting the Earth’s temperature rise to 1.5 °C – the aspirational goal of the Paris Climate Agreement – is thus not only crucial for saving the majority of the world’s plant and animal species as well as safeguarding low-lying island states from sea level rise and the poorest countries from climate extremes18, but also a precautionary step to prevent triggering climate tipping points. Nevertheless, countries must raise their level of ambition by over five times to reach the 1.5 °C goal.

According to the 2018 special report by the Intergovernmental Panel on Climate Change of the United Nations, the remaining carbon budget, to stand a reasonable chance (66%) of limiting warming to 1.5 °C would be depleted by around 2030. The panel’s conclusions were, however, criticized for being too conservative. Considering, for example, an upper estimate of a wide range of potential Earth system feedbacks, humanity might have already exceeded the remaining budget to limit warming to 1.5 °C, (66% probability). Moreover, mitigation pathways compatible with 1.5 °C imply the deployment of negative emissions technologies (e.g., bioenergy production with carbon capture and storage). Science and policy advances in these fields are currently far from ideal.

Climate tipping points

The Earth’s climate system is formed by large-scale components characterized by a threshold behavior known as tipping elements. Put another way, climate tipping elements are supra-regional constituents of the Earth’s climate system that may pass a tipping point. The Greenland ice sheet and the Amazon rainforest are examples of tipping elements. A tipping point is 'a threshold at which small quantitative changes in the system trigger a non-linear change process that is driven by system-internal feedback mechanisms and inevitably leads to a qualitative different state of the system, which is often irreversible'.

What are key factors affecting risk levels?

Climate change is a highly complex phenomenon affected by many factors. We may classify them into four categories to better discern the various areas where action is possible:

  • The risk is directly related to the release of greenhouse gases in the atmosphere through human activity. Carbon dioxide mainly results from the burning of fossil fuels for energy and transport. In turn, this is a factor of population growth and unsustainable production and consumption models. As to methane emissions, they largely relate to large-scale animal farming, driven by demand for meat, dairy, and wool.
  • Some ecosystems store large amounts of carbon, particularly forests and coastal marine ecosystems, and their destruction could result in the large-scale release of greenhouse gases in the atmosphere.
  • The third factor is our capacity for global coordination to reduce emissions. This may be positively impacted by a better understanding of tail-end climate risk and climate tipping points, increasing the sense of urgency and prompting faster action.
  • Finally, the risk of catastrophic climate change is increased by insufficient knowledge and understanding of impacts and vulnerability, in turn affecting our ability to build resilience.

The complex and interrelated nature of global catastrophic risk suggests an integrated research agenda to address related challenges and dilemmas and ensure human development and the protection of the non-human living beings that enable life on the planet to thrive. One such related challenge is the use of solar radiation management techniques (namely, stratospheric aerosol injection) to reduce the risk of catastrophic climate change, which might harm in other ways.

The impact of the COVID-19 pandemic on climate change

The COVID-19 global health crisis will likely lead to a reduction in global carbon emissions in 2020. But how could the pandemic affect climate change in the mid to long-terms?


Some fear that the virus will weaken climate action. There is a serious risk that political and public attention to climate issues will dramatically decline in the face of the pressing, severe economic and social consequences of the crisis. The next conferences of the parties of the United Nations Framework Convention on Climate Change and the Convention on Biological Diversity, which would take place in the end of 2020 but have been postponed due to the pandemics, are critical for climate change mitigation and nature protection, as new emissions reduction commitments are expected to be presented and new global agreements on biodiversity concluded. In addition, governments may be tempted to pursuit short-term easy fixes with negative environmental impacts, e.g., rolling back environmental standards and subsidising fossil fuel- heavy industries to stimulate the economy, prioritising indiscriminate economic growth over environmental sustainability imperatives.


In China, by the end of March, demand for energy and carbon emissions were already returning to normal levels following a 25 per cent reduction in emissions. The country may also be considering relaxing emissions standards to help hard-hit carmakers. Moreover, the economic impact of the crisis may undermine investments in clean energy and further complicate the transfer of financial resources to assist developing countries in their climate change mitigation efforts.


Others believe that the COVID-19 crisis can be a turning point, giving rise to a greener future, as the economic recovery packages that are being prepared by many countries around the world offer an opportunity to re-build economies and societies towards sustainable modes of production and consumption.

"…global warming makes conditions more favourable to the spread of some infectious diseases and air pollution makes people more vulnerable to infection."

Climate change, biodiversity loss and human health

The COVID-19 global health crisis urges us to rethink our relationship to nature and the non-human species with which we share the planet. The coronavirus has been attributed to anthropogenic interferences on the natural world such as deforestation, a major contributor to climate change, encroachment on animal habitats, and biodiversity loss, which is also driven by climate change among other factors. The pandemic is a reminder of our enmeshment in a more-than-human world. It also calls our attention to the critical links between climate change and biodiversity loss, and their impacts on human health.

By eroding wild spaces for agriculture and changing the climate – thus forcing animals to find food and shelter close to people or migrate to escape heat – we are creating new opportunities for pathogens to get into new hosts. By trading and consuming wild animals, we increase the likelihood that zoonotic viruses will jump to humans.

Moreover, and although there is no direct evidence that climate change is influencing the spread of the new coronavirus, we know that global warming makes conditions more favourable to the spread of some infectious diseases and that air pollution makes people more vulnerable to infection40. We also know that when biodiversity declines, the species that thrive are the ones that are best at transmitting diseases e.g., bats and rats. As current species extinction rates have no parallel in human history, there are strong reasons for concern. Finally, attention is also needed on the thawing of the Arctic’s permafrost as a result of global warming and the possibility that viruses and bacteria once buried in the region are released.

Future policies must thus integrate climate, biodiversity and health considerations as well as the needs and rights of the non-human living beings with which we share the Earth.

Reviewed by

Joana Castro Pereira

Dr Joana Castro Pereira is a Postdoctoral Researcher at Portuguese Institute of International Relations, NOVA...

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