The studies cited below are either reports from intergovernmental research bodies (such as the IPCC) or published studies in peer-reviewed scientific journals. Reports by intergovernmental research bodies such as the IPCC presuppose a high degree of scientific consensus, while journal articles represent the latest scientific insights and results. This summary was written in 2019. For more and more recent sources, please see Sources for Planet-Amateurs.
Global warming so far
Compared to pre-industrial times, the planet has so far heated up by 1.1°C (WMO 2019). These 1.1°C represent an average between global atmospheric and oceanic temperatures. In some parts of the world warming is therefore already higher. The ecological consequences of 1.1°C of warming are, among others:
1. Rapidly melting glacial and sea ice, and rising sea levels (WMO 2019, NASA 2018).
2. Ocean warming and acidificaton. Acidification happens because the oceans absorb excessive CO2 from the atmosphere. As a result, marine life such as corals, shellfish and fish die, which other organisms (including humans) need to nourish themselves.
3. More frequent and more extreme weather events (Herring et al. 2018, WMO 2019).
4. Soil degradation and desertification (UNCCD 2019, WAD 2018). This means that soils lose their fertility/productivity and water reserves. The consequences are, as one can imagine, crop failures and, as a result, food and drinking water shortages – for both humans and animals alike.
5. The mass extinction of various plant and animal species (see “Species extinction” below).
Species extinction and biodiversity loss
Scientists speak of our current era as the “sixth mass extinction” in the history of our planet (Ceballos et al. 2017). The last “fifth mass extinction” took place about 65 million years ago (caused, among other factors, by an asteroid strike), with the dinosaurs becoming extinct. Mass extinction is measured according to the average extinction rate of plant and animal species. Plants and animals also die out “naturally”. This is part of evolution. However, scientists believe that the current extinction rate is more than 100-1000 times higher than the natural so-called “background extinction” rate. Between 1970 and 2016, globally monitored population sizes of mammals, fish, birds, reptiles, and amphibians have declined an average of 68% (WWF 2020) Currently, one million animal and plant species are threatened with extinction – many of them in the coming decades (IPBES 2019). According to the U.N. Convention on Biodiversity, up to 150 species are lost every day! That as such is already terrible. In addition, human survival deeply depends on the preservation of biodiversity. Humans need biodiversity to feed themselves, to breathe clean air, to manufacture medicines – and, last but not least, to admire and enjoy it! According to the Intergovernmental Science-Policy Panel on Biodiversity and Ecosystem Services (IPBES), “we are eroding the very foundations of our economies, livelihoods, food security, health and quality of life worldwide” (IPBES 2019). Species extinction is therefore just as threatening as global heating – and both are intertwined. Because – what drives this extreme loss in biodiversity? According to the IPBES report, the main causes are, in descending order:
- Changes in land and sea use – e.g. industrial agriculture and urbanization. The meat and dairy industry is of particular importance here. 83% of the global agricultural area is currently used for the production of animal products (meat, dairy, fish and eggs). The world population, however, only obtains 18% of its calories and 37% of its proteins from animal products (Poore & Nemecek 2018). Large forest areas of the Amazon, for example, are currently being cleared in order to develop agricultural land for the cultivation of soy and other forms of livestock feed.
- Direct exploitation of organisms – e.g. through unsustainable hunting and fishing practices.
- Climate change – e.g. ocean acidification and desertification.
- Pollution – e.g. oceanic pollution through (micro-)plastic and land pollution through pesticides
- Invasive alien species – i.e. plants and animals that humans transport into areas and ecosystems where they don’t belong and therefore cause damage.
Both global warming and species extinction are not subject to scientific forecasts but are happening already! This has ramifications for people worldwide. The interrelated human consequences of the previously mentioned phenomena are:
- Illness, hunger and death (DARA 2012, Mukerji 2019, WHO 2009, WMO 2019) – e.g. due to extreme weather events, food and drinking water shortages, air and drinking water pollution, environmental toxins, etc.
- Economic and non-economic loss (Hsiang et al. 2017, Serdeczny et al. 2016, Warner et al. 2013, WMO 2019) – e.g. homelessness due to extreme weather events, or loss of cultural heritage and traditional lifestyles due to the destruction of natural habitats, etc.
- Social and political instability (Buhaug 2016, Sellers et al. 2019) – e.g. conflicts due to resource and food shortages. Many factors come together here.
- Displacement (Berchin et al. 2017, Warner et al. 2009) – due to a combination of the aforementioned factors.
Unfortunately, there is often a huge gap between people and countries who – according to ecological footprint measures – are predominantly causing global heating and species extinction, and the people, countries and species who are involuntarily experiencing its main consequences at the moment! It is also for this reason that the current climate movement is often called “Climate Justice Movement”.
Scientific forecasts for the future are terrifying. Climate skeptics in particular like to argue that future forecasts are based on scientific models and are therefore not 100% guaranteed. That’s true. However, in our everyday lives, we constantly rely on such models. Every car’s fuel gauge represents a model which – based on empirical facts – provides a future forecast of when we are likely to run out of fuel. The same applies to medical diagnoses (e.g. stages of an illness) or the weather forecast. Sometimes they are also wrong. Sometimes the weather is a little better than predicted, sometimes worse. Sometimes an illness develops better than predicted, but sometimes, unfortunately, worse. The same applies to climate change. And, we should bear in mind that previous scientific forecasts have underestimated rather than overestimated the speed and severity of climate change! For example, the majority of previous scientific studies had predicted that arctic permafrost would approximately start to melt in 2090 (IPCC 2014). In 2019, however, an expedition by scientists from the University of Alaska showed that this process has already started – 70 years earlier than expected! And why is it so important if and when the permafrost melts? Because permafrost melting is associated with the release of other greenhouse gases (such as methane) and thus accelerates global heating considerably (see also ‘geo-physical feedback effects’).
So what about the forecasts?
In its last special report from 2018, the IPCC warns that all climate change associated risks (sea level rise, species dying, extreme weather, etc.) are projected to be significantly lower for a warming of 1.5°C than for a warming of 2°C. The IPCC therefore insists that global warming must be kept “well below 2°C” – and ideally stabilized at 1.5°C. This was set as international goal at the UN Conference of the Parties (COP) in 2015 in Paris. As a reminder, global warming has already reached 1.1°C (WMO 2019). In addition, there is always a time lag between the moment when greenhouse gases are emitted into the atmosphere and the moment when they develop their full warming potential (Zickfeld & Herrington 2015). In concrete terms, this means that the greenhouse gases we have emitted throughout recent years are yet to develop their full warming potential! Accordingly, the planet would still continue to heat up if we became carbon neutral by tomorrow already. And, of course, we are far from becoming CO2 neutral. On the contrary, instead of reducing emissions, global CO2 emissions have risen steadily throughout recent years – despite the Paris climate targets! What about the Netherlands in this context? CO2 emissions in the Netherlands have not increased in recent years, but the average Dutch person causes almost twice as much CO2 emissions than the average world citizen (see World Bank Data).
What will happen next?
In a study from 2017 (published in the renowned journal Nature Climate Change), scientists statistically evaluated how the main emission drivers (per capita GDP, carbon intensity and population growth) will develop worldwide throughout the next 80 years. Importantly, the study also considers existing policy measures to reduce emissions. The study concludes that the likelihood of limiting global warming to 1.5° C within the next 80 years is currently 1%!!! It is much more likely that the planet will heat up between 2.0 and 4.9 ° C in the next 80 years. The statically most probable temperature forecast (the so-called median) is 3.2°C (Raftery et al. 2017)! In short, we are on a global warming course well above what scientists consider a manageable risk (well below 2°C). We are already seeing devastating effects at 1.1°C. All of this does not yet include another risk factor – that of geophysical feedback effects.
Global heating as domino effect – the risk of geophysical feedback effects
In addition to the fact that humans and animals are already suffering and dying from the effects of global heating NOW, feedback effects are THE argument why we have to reduce greenhouse gas emissions as quickly as possible. We can think of feedback effects as a kind of mixture between a domino effect and a vicious circle. The tilting of one stone sets into motion the tilting of the next, whereby the effect accelerates stone by stone. As soon the first stone has tipped, it is impossible to prevent all other stones from tipping as well. The same applies to global heating. Scientists estimate that our global climate system will reach a tipping point somewhere between 1°C and 2°C of warming (Lenton et al. 2019). Stone 1, which has been wobbling for some time, tilts and knocks down stone 2, 3, 4 and so on. What concretely does that mean? A good example is the so-called “ice albedo feedback”. Global warming is causing ice and snow to melt all over the world. For example, it is causing the melting of Arctic ice sheets. These arctic ice sheets in turn play an important role in our climate system because they reflect sun radiation. The more ice melts, the more sun rays are no longer reflected back but instead reach the surface of the sea, thus warming up water. This, in turn, causes more ice to melt – triggering a vicious cycle. Yet, the ice albedo effect is only one among many feedback effects. In addition, there are also methane releases due to melting permafrost, wildfires (=more emissions), water vapor, and many more. As for the domino effect: Scientists estimate that, from a certain (not too far away!) temperature tipping point onward, different feedback effects would reinforce each other, thus causing the planet to quickly heat up by itself! Scientists call this scenario a so-called “hothouse earth” path (see also this video by the Stockholm Resilience Center). “This pathway would be propelled by strong, intrinsic, biogeophysical feedbacks difficult to influence by human actions, a pathway that could not be reversed, steered, or substantially slowed” (Steffen et al. 2018). In other words, humans are currently causing global heating. Above a certain temperature limit, the planet will heat up by itself – and possibly very quickly and without humans being able to stop it!
What do “hotter conditions” mean?
It is difficult to predict exactly what will happen as global warming continues. A study from 2017 estimates that any global warming beyond 1.5°C would be “dangerous”, beyond 3°C would be “catastrophic”, beyond 5°C “unknown” – including “existential threats to EVERYONE” (Xu & Ramanathan 2017). The same study estimates that 4°C of warming would expose “approximately 47% of the global land area and almost 74% of the world’s population to deadly heat”. “Deadly heat” in this context means “existential risks to humans and mammals alike unless massive adaptation measures are implemented” (which in turn would have to happen rapidly and require enormous resources). In this context, it is worth bearing in mind that we are already witnessing the devastating effects of global warming at 1.1°C (see “Global warming so far”).
And how likely is this all?
Global ecosystems are complex and there is a risk to both over- AND underestimate global heating tendencies. As already described, the scientists Raftery et al. 2017 calculate that, considering today’s climate change mitigation efforts, it most probable that the planet will heat up between 2°C and 4.9°C within the coming 80 years. Xu & Ramanathan 2017 assign a 50 percent probability to the scenario that global warming will reach “dangerous” levels of more than 1.5°C within the coming 30 years (by 2050). They also assign a 50 percent probability to the scenario of “catastrophic” warming levels of more than 3°C within the coming 80 years. To the last risk level “unknown” – which “includes existential threats for EVERYONE” – they assign a probability of 5%. The latter sounds like little, but it still implies a probability of 1 in 20 cases! Would you board a plane under these conditions?
What we can take away from the cited studies is
People, animals and ecosystems are already suffering and dying from global heating, resource exploitation and pollution. Scientists consider it plausible and even likely that much of the global human (and animal!) population will be exposed to life-threatening levels of heating within the coming eighty years! That is within the lifespan of today’s young generations! The only means to avert this development are immediate, more consistent and effective global climate policies – and to do that, it’s time to raise the alarm worldwide!