All facts in 10 minutes

In 10 years, do you want to be among those who regret that they have not informed themselves? Or to those who have tried everything to save the earth as it was for themselves and their children? Get informed now, it takes only 10 minutes. If you have doubts about the climate change read this article and the references therein. In summary, the latest evaluation of world-wide studies is based on over 5000 references [1]. This is an impressive number that corresponds to many thousands of person-years of work and their findings are shared by all independent scientists.

What will happen (our current path)

Climate change is not coming in the future, it is in full swing. In 2017, global warming exceeded 1°C compared to before 1900 [1,2]. At the earth poles over 3°C had been reached already earlier (2013) . In northern Europe, 5°C higher average temperatures were measured in 2018 [4]. This warming may not seem high, but it is enough to melt polar ice, warm the oceans and cause weather extremes (storms, El Niño, drought, forest fires, etc.), including also the northern hemisphere. In 2018 unusually devastating wildfires occured Sweden, Norway, Latvia, Germany, Great Britain and Ireland [4]. Likewise, there were severe losses due to droughts, so that, for example, the German Federal Minister Klöckner on August 22, 2018 classified the extreme drought of 2018 as an exceptional weather event of national proportions and hundreds of millions were spent to help farmers (precipitation was the lowest since the beginning of the weather record [5,6]). But this has not been an isolated case: the last few years since the weather record are regularly the warmest ever (for example, the four warmest years in 2015, 2016, 2017 and 2018 were [4,7]).

GLobal CO2 emissions: We are on the red path, which is referred to as the “worst-case”. The blue line represents readings from recent years (R. Kopp, Rutgers Climate Institute; updated by R. Kopp after Kopp et al. 2014 [8], CC BY-NC 4.0).

Currently we are on the path that is referred to as the worst-case scenario. As can be seen in the figure above, CO2 emissions are rising steadily. In the figure, the blue line (“Historical”) represents measured values and the red line (referring to climate scenario RCP8.5, our current path) refers to values predicted in 2011. We are pretty much following the model predictions for the “worst case” scenario “RCP8.5”. This results in a global warming of 4°C by 2100, as can be seen in the figure below:

Global temperature increase used in IPCC-AR5 presented by the RCPs. The values in parentheses represent the number of GCMs. Source: Knutti and Sedlácek (2013). 
Global warming for different climate scenarios (RCPs). Currently we are heading to a warming of 4 ° C by 2100, the red line, corresponding to scenario RCP8.5). After Knutti and Sedlácek (2013 [9]).

But what does that mean for us, what are the consequences? In 2018, the IPCC evaluated more than 5,000 scientific sources and summarized their findings [1]. Hence, the IPCC report is not a single opinion, but a summary of the accumulated knowledge of humanity on this subject (note that doubts about climate change as a man made problem do not come from scientists [10] but from other stakeholders or politicians, usually representing industry [11]).

As we continue to move towards the worst-case scenario (the so-called RCP8.5 scenario), we will reach 4 ° C global warming by 2100 (see figure left; RCP8.5 (Representative Concentration Pathway 8.5) means that one square metre surface of the earth will be heated by an additional 8.5 Watt in the year of 2100). But what impact has a gloabl warming by 4°C for us? Will it cause notable changes for our livelihoods? The IPCC has not evaluated the consequences for this temperature, the costs for mankind would be intolerable at 4°C. Instead, only the consequences for a 3°C warming were summarized by IPCC and presented as follows [chapter 3, p. 280ff in reference 1]:

“Global warming of 1.5°C is reached by 2030 […]. Starting with an intense El Niño–La Niña phase in the 2030s, several catastrophic years occur while global warming starts to approach 2°C. There are major heatwaves on all continents, with deadly consequences in tropical regions and Asian megacities […]. Droughts occur in regions bordering the Mediterranean Sea, central North America, the Amazon region and southern Australia. […] Intense flooding occurs in highlatitude and tropical regions, in particular in Asia, following increases in heavy precipitation events. […] Major ecosystems (coral reefs, wetlands, forests) are destroyed over that period, with massive disruption to local livelihoods. An unprecedented drought leads to large impacts on the Amazon rainforest […]. A hurricane with intense rainfall and associated with high storm surges destroys a large part of Miami. A two-year drought in the Great Plains in the USA and a concomitant drought in eastern Europe and Russia decrease global crop production, resulting in major increases in food prices and eroding food security. Poverty levels increase to a very large scale, and the risk and incidence of starvation increase considerably as food stores dwindle in most countries; human health suffers […]. There are high levels of public unrest and political destabilization due to the increasing climatic pressures, resulting in some countries becoming dysfunctional. […] Massive investments in renewable energy often happen too late and are uncoordinated; energy prices soar as a result of the high demand and lack of infrastructure […].

Global mean warming reaches 3°C by 2100 but is not yet stabilized despite major decreases in yearly CO2 emissions, as a net zero CO2 emissions budget could not yet be achieved and because of the long lifetime of CO2 concentrations. The world as it was in 2020 is no longer recognizable, with decreasing life expectancy, reduced outdoor labour productivity, and lower quality of life in many regions because of too frequent heatwaves and other climate extremes […]. Droughts and stress on water resources renders agriculture economically unviable in some regions. […] Poverty rates reach new highs. Major conflicts take place. Almost all ecosystems experience irreversible impacts, species extinction rates are high in all regions, forest fires escalate, and biodiversity strongly decreases, resulting in extensive losses to ecosystem services. These losses exacerbate poverty and reduce quality of life. […] Aggregate economic damages are substantial, owing to the combined effects of climate changes, political instability, and losses of ecosystem services. The general health and wellbeing of people is substantially reduced compared to the conditions in 2020 and continues to worsen over the following decades.”

This is the description by the IPCC for 3°C warming. As mentioned above, we are heading for 4°C. Hence the level of catastrophic events and unimaginable chaos expected at 3°C will in fact be substantially higher.

Other organizations have looked at other consequences of climate change, such as climate-related migration (caused by drought, climate-induced extreme weather events, sea leve rise). The International Organization for Migration has estimated in its latest annual report [12], based on hundreds of studies, that by 2050, the annual number of refugees worldwide will reach 405 million (i.e. per year). This is almost equivalent to the population of the USA (327 million) or the EU (512 million). Imagine each year the population of the USA would be migrating into other parts of the world, searching for new homes, food and labour. By comparison, even in the ‘refugee year’ of 2015, only 2-4 million people immigrated to the EU [13] and this already caused some unrest in many EU countries. Currently, there are approximately 25 million climate-related refugees worldwide every year (118 affected countries [14]). In recent decades, dramatic climate extremes, for example in sub-Saharan Africa, have become more and more frequent in Africa [15,16]. For people who fear migration and doubt climate change, it may be of interest that geographically, the best alternative to migrate to from these regions is evidently Europe (a similar situation appllies for South and North America).

Other consequences include the so called sixth mass extinction in the Earth’s history [17], which describes the dramatic recent decline of species and our plant and which is largely due to global warming and other, related human activities (such as massive deforestation). The last mass extinction 66 million years ago caused the extinction of the dinosaurs by a meteor impact; about 75% of all species disappeared [18]. The UN reported in 2019 [19] that 47% of all mammals (marine mammals and bats not considered) 23% of endangered bird species were already now adversely affected by climate change. The UN estimates that 1/8th of all species are on the edge of extinction [19].

Why is climate change irreversible when we reach more than 1.5°C? This is due to so-called tipping points. For example, the atmosphere and the polar ice reflect a large part of the solar radiation [20], the so-called albedo effect. By increasing the CO2 concentration, the reflection of radiation from the sun in the atmosphere and that of the dwindling polar ice is more and more reduced, resulting in an accelation of global warming. Another tipping point is the formation of clouds, which is partly CO2 dependent. Increasing concentration of CO2 can disrupt cloud formation (in particular stratocummuls clouds), which is expected to result in 8°C warming on the earths surface once this tipping points is reached, due to less reflection of solar radiation by clouds [21]. When you look at (unedited) photographs of our planet, you may recognise that a substantial fraction is covered by clounds. There are many other similar mechanisms [22, 23]. Once such tipping points are surpassed, an automatism starts and the earth continues warming even if we completely cut CO2 emissions.

What do we need to do?

The answer is simple: We need to be CO2 neutral within at least 10 years [1]. Because at the current emission rate, we will have emitted the maximum amount of CO2 (420 Gt) in 10 years, which may enable us to still prevent irreversible changes and to stay within 1.5°C of warming [1; some recent studies, however, indicate that we may have even less than 10 years*]. The alternative would be to wait until the chaos breaks over us; then we will pay a much higher price. So we will pay in any case, either less now or many times more in the near future. Our best chance today is to shape how the world should look like, so that we do not exceed the 1.5°C limit promised in the Paris Agreement. Only this will ensure that we do not reach tipping points. After all, how are we going to be able to achieve comprehensive economic change later on, when at the same time we are struggling to secure our livelihoods, while there are social and political unrests, even stronger storms, floods, mass migration to the least affected regions of the world, when every second person in our countries may be a climate refugee that may not speak our language? Moreover, it is an unique economic opportunity to help shape developments and not be left behind by other countries that have committed to climate change much earlier (such as China, which has been heavily investing in the renewable energy sector in the last decade).

* Recent studies indicate that in current climate models positive feedback mechanisms and tipping points have not been included sufficiently, leading to an underprediction of future global warming. This is supported by current observations, for example thowing of permafrost (and hence release of methane) in Canada has recently been found to have surpassed levels that were predicted by climate models only for the year 2090. For details see this article.

How do we do it?

Every person is capable of much more than he believes. And every person has more power than he thinks. Many important events in human history were shaped by single, perseverant individuals. You too can achieve a lot (just think of how much that little Swedish girl has achieved). One step is to reduce your own emission, which is easier than you may think (see this article). But it is not enough to try to become a climate neutral person; we also need political pressure to steer economic decisions upon which individuals have no influence (e.g. industry shift to carbon neutral production). In this context it may be noted that technically the switch to renewable energy is not a big problem (as can be seen in China now). However, in some countries, such as Germany, ambitions have been actively stopped in favour of the coal industry, which meant that many jobs in the solar industry were lost (see talks by Prof. Bruno Burger, Frauenhofer ISE, and Prof. Volker Quaschning, HTW Berlin, both only available in German, unfortunately). Specifically, you can do the following:

Become politically more active:

  1. Search for a few favorite members of your local and national parlament and write them, inform them (unfortunately only few people know the most relevant facts, although many think they know them) and ask them to vigorously progress the prevention of climate change.
  2. Always go voting, and vote for a party that massively pushes the prevention of climate change, if there is none, join a party yourself and push it to do just that.
  3. Organize demonstrations or participate in them, so that the general public and politicy makers realize that the issue of climate change is urgent.

Become active in private:

  1. Inform friends, acquaintances and work colleagues about the urgency of climate change.
  2. Encourage them to take action, use your network!
  3. Inform yourself about the main sources of greenhouse gas emissions (e.g. read this article).
  4. Change your electricity power provider and go to vendors who use 100% renewable energy. You may even save money, because solar power is now the cheapest source of energy [24]! Many of them also offer climate neutral gas.
  5. Do not fly unnecessarily whenever the train is equally fast (and when you don’t feel like spending hours waiting in the airport).
  6. Fly more rarely (or not at all): Instead of going for several short trips per year, fly just once and do a longer vacation experiencing your destination properly and with leisure. Or why not try to travel accross Europe or Canada by train.
  7. Use your bike or public transport.
  8. Eat less meat and dairy. The production of beef and dairy causes particularly high greenhouse gas emissions.
  9. Safe cost for heating (e.g. by using programmable thermostats).
  10. Do not blindly consume, rather buy quality products that hold; don’t consume products that will soon end up in the bin (the production and transport of many products is very CO2 intensive).
  11. Buy products that don’t support deforestation (for example buy products without palm oil).

Do you want to know more or do you still have doubts?

If you don’t trust what you just read (which is good in times of fake news), then start reading the IPCC report from 2018 [1], in particular chapter 3. Be aware that this is just a summary of more than 5250 sources, which correspond to thousands of years of scientific work. For a scientist the IPCC report is an impressive scientific achievement. If you have more time, do you own research. There are literally thousands of excellent sources out there, so make up you own picture. But try to rely on peer reviewed scientific journals or reports from governmental agencies or institutes, as on webpages everybody can post what one likes, without any review. There are also pseudoscientific publications by so called Thinktanks, which are industry funded institutions, aimed at promoting opinions or to spread doubt about climate change. So look who funded the work.

Corrections or ideas for improvements are very welcome, please just send an email to info (a)


  1. International Panel on Climate Change (IPCC) 2018. Global warming of 1.5 °C. Special report. Online (a full list of references used by IPCC can be found here)
  2. Haustein, K. et al. 2017: A real-time global warming index. Scientific reports 7: 15417. Online
  3. Christensen J.H. et al. 2013: Climate phenomena and their relevance for future regional climate change supplementary material. In: Climate change 2013: The physical science vasis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker T.F., D. Qin, G.K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1217–1308.
  4. World Meterological Organisation 2019. WMO statement on the state of the global climate in 2018. WMO-No. 1233. Online
  5. Imbery F. Friedrich K., Haeseler S., Koppe C., Janssen W., Bissolli P. 2018 Vorläufiger Rückblick auf den Sommer 2018 – eine Bilanz extremer Wetterereignisse. Deutscher Wetterdienst, Abteilungen für Klimaüberwachung und Agrarmeteorologie. Online
  6. Institut für Pflanzenproduktion und Betriebswirtschaft 2018. Erntebbericht MV 2018. Online
  7. NASA 2019. 2018 fourth warmest year in continued warming trend, according to NASA, NOAA. Online
  8. Kopp R. et al. 2014. American Climate Prospectus. Economic Risks in the United States. Part V. Insights for climate risk management. Risky Business Project report. Online
  9. Knutti R., Sedlacek J. 2013. Robustness and uncertainties in the new CMIP5 climate model projections. Nature Climate Change 3: 369–373. Online
  10. Cook J. et al. 2013. Quantifying the consensus on anthropogenic global warming in the scientific literature. Environ. Res. Lett. 8: 031003. Online
  11. DiMento J. and Doughman P. 2017. Climate Change: What it Means for Us, Our Children, and Our Grandchildren. Cambridge, MA: MIT Press, pp. 25-29.
  12. International Organization for Migration (IOM) 2018. World migration report 2018. Online
  13. EU 2017. EU migrant crisis: facts and figures. Online
  14. IDMC / Norwegian Refugee Council 2017. Global report on internal displacement. Online
  15. Paeth H. et al. 2010. Meteorological characteristics and potential causes of the 2007 flood in sub-Saharan Africa. International Journal of Climatology 31: 1908–1926.
  16. Taylor C.M. et al. 2017. Frequency of extreme Sahelian storms tripled since 1982 in satellite observations. Nature 544: 475–478. Online
  17. Ceballos G. et al. 2015. Accelerated modern human–induced species losses: Entering the sixth mass extinction. Science Advances 1: e1400253. Online
  18. Bambach R.K. 2006. Phanerozoic biodiversity mass extinctions. In: Annual Review of Earth and Planetary Sciences. 34: 127–155.
  19. IPBES (UN Environment Programme) 2019. Global assessment of biodiversity and ecosystem services. Online; Answers to questions and videos are also available here.
  20. Donohoe A., Battisti D. 2011. Atmospheric and Surface Contributions to Planetary Albedo. Journal of Climate 24: 4402-4418. Online
  21. Schneider T. et al. 2019. Possible climate transitions from breakup of stratocumulus decks under greenhouse warming. Nature Geoscience 12: 163–167. Online
  22. Lenton T.M. et al. 2007. Tipping elements in the Earth’s climate system. PNAS 105: 1786-1793. Online. Online
  23. Wikipedia article “Tipping points in the climate system” (with sources): Online
  24. Frauenhofer Institut 2018. Photovoltaik und Onshore-Wind sind günstigste Technologien in Deutschland. Online

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