Why act?

Climate change will transform our civilization in a fundamental way. Without quick and effective action, we will see increasingly severe consequences for humans and our societies. Extreme heat becomes more frequent, water resources and food production become less reliable, diseases move into new ranges, sea levels rise and infrastructure keeps being damaged from floods and storms. We provide some basics on climate change and a brief overview what science tells us about the potentially devastating effects of climate change if we don’t act.

“Climate change is not an environmental problem – it is a threat to human lives and livelihoods”

Why act?

Climate change will transform our civilization in a fundamental way. Without quick and effective action, we will see increasingly severe consequences for humans and our societies. Extreme heat becomes more frequent, water resources and food production become less reliable, diseases move into new ranges, sea levels rise and infrastructure keeps being damaged from floods and storms. We provide some basics on climate change and a brief overview what science tells us about the potentially devastating effects of climate change if we don’t act.

“Climate change is not an environmental problem – it is a threat to human lives and livelihoods”

At the moment we are likely heading towards more than 3°C global warming, represented by the ‘current policies’ scenario in the graph. Even if all commitments made in the Paris Agreement were met – and many countries are far from that – warming would likely reach close to 3°C (‘pledges & targets’ scenario)..

Global average temperatures are, in fact, already close to 1°C above pre-industrial times [this normally refers to before 1880]. We are already seeing some impacts of climate change. Not acting does not mean we can just continue to live the lives we know today. There is no ‘business-as-usual’. Here we provide some basics on climate change and a brief overview what science tells us about the potentially devastating effects of climate change if we don’t act.

How does global warming work…?

Life on Earth depends on energy coming from the Sun. About half the light reaching Earth’s atmosphere passes through the air and clouds to the surface, where it is absorbed and then radiated upward in the form of infrared heat. About 90 percent of this heat is then absorbed by the greenhouse gases and radiated back toward the surface.

…so where is the problem…?

The concentration of greenhouse gases in the atmosphere has changed over the last century. The consequences of changing the natural atmospheric greenhouse are difficult to predict, but on average, Earth will become warmer with a wide range of effects described in more detail below.

Taken as a whole, the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time.

Intergovernmental Panel on Climate Change

…and is it really manmade?

Sceptics of manmade climate change offer various natural causes to explain why the Earth has warmed around 1°C since 1880. But can these account for the planet’s rising temperature? Watch to see how much different factors, both natural and industrial, contribute to global warming, based on findings from NASA’s Goddard Institute for Space Studies.

Does it matter if it is manmade?

Yes, it does. Because the answers to the observed changes in climate are very different depending on the cause: If there were other causes of the problem, we would need to research into possible countermeasures – or simple accept the inevitable. Manmade global warming means we can and need to stop activities that are causing this warming, such as burning fossil fuels.

Why cold winters still make sense in a warming climate…


Weather refers to the more local changes in the climate we see around us, on short timescales from minutes to hours to days to weeks. Examples are familiar – rain, snow, clouds, winds, thunderstorms, heat waves and floods.


Climate refers to longer-term averages (they may be regional or global), and can be thought of as the weather averaged over several seasons, years or decades.


“Weather is your mood and climate is your personality.”

Professor Marshall Shepherd, University of Georgia

Differences in weather across years are normal. There have always been particularly cold or warm winters, long or short rainy seasons or sudden cold spells in the middle of summer. Even with increasing pressure from greenhouse gases on the climate, surface temperatures from year to year will fluctuate depending on the naturally variable forces at work around the globe. Global warming does not mean there is a linear, year-to-year increase in temperatures, but an average increase that can lead to all kinds of local weather effects.

What will happen with a changing climate – and what it means

Scientists worldwide agree that

On average, Earth will become warmer. Some regions may welcome warmer temperatures, but others may not.

Warmer conditions will probably lead to more evaporation and precipitation overall, but individual regions will vary, some becoming wetter and others dryer.

A stronger greenhouse effect will warm the oceans and partially melt glaciers and other ice, increasing sea level. Ocean water also will expand if it warms, contributing further to sea level rise.

Meanwhile, some crops and other plants may respond favourably to increased atmospheric CO2, growing more vigorously and using water more efficiently. At the same time, higher temperatures and shifting climate patterns may change the areas where crops grow best and affect the makeup of natural plant communities.

But these are just some of the physical impacts that are expected. And these changes will impact our societies in different ways, affecting our infrastructure, our ability to grow food and where we can live. The effects are complex, as the impacts are not distributed uniformly across the planet and depend on many variables, including which level of temperature increase we are expecting. Click on the pictures to get an overview of the main effects of global warming and a discuss what this means for human society.

tipping point in the climate system is a threshold that, when exceeded, can lead to large changes in the state of the system. Potential tipping points have been identified in the physical climate system, in impacted ecosystems, and sometimes in both.

The Intergovernmental Panel on Climate Change (IPCC) introduced the idea of tipping points two decades ago. At that time, these ‘large-scale discontinuities’ in the climate system were considered likely only if global warming exceeded 5 °C above pre-industrial levels. Information summarized in the two most recent IPCC Special Reports (see below) suggests that tipping points could be exceeded even between 1 and 2 °C of warming.

Find out more about these tipping points and their consequences by clicking on the picture.

The scientists

The Intergovernmental Panel on Climate Change (IPCC) is the United Nations body for assessing the science related to climate change. The objective of the IPCC is to provide governments at all levels with scientific information that they can use to develop climate policies. Thousands of scientists from all over the world contribute to the work of the IPCC. IPCC reports summarise published scientific papers and are reviewed in a transparent process by experts and governments. The assessment identifies the strength of scientific agreement and thus provides a solid overview of what is known about drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks.

In a nutshell – The science behind it

IPCC 1.5°C Special Report


  • We already have caused around 1°C of global warming
  • We can already observe impacts on natural and human systems
  • Without further action, warming will reach 1.5°C between 2030 and 2052
  • Impacts will be lower at 1.5°C compared to 2°C, but are already substantial, for example, average sea level rise will be at least 10 cm less by 2100 than for 2°C, with 10 million fewer people facing risks as a result
  • To achieve a 1.5°C target, net CO₂ emissions have to be reduced by 50% by 2030 on 2010 levels, and reach ‘net-zero’ around 2050


Read the full report here
Read a six page summary here

IPCC Ocean and Cryosphere Special Report


  • The ocean has warmed throughout its depth and is continuing to do so at an increasing rate
  • The circulation system known as the Atlantic Meridional Overturning Circulation (AMOC) will weaken and the impacts of this are hard to predict
  • Sea level has risen between 12 and 21 cm on a global average since 1902
  • Sea level is expected to rise by 29 to 59 cm (low emissions) and 61 to 110 cm (high emissions) by 2100
  • Warming in recent decades has resulted in ice mass loss from mountain glaciers worldwide


Read the full report here
Read a three page summary here

IPCC Fifth Assessment Report


  • Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history
  • Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia
  • The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen
  • Changes in many extreme weather and climate events have been observed since about 1950
  • Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems

Read the full report here

IPCC Special Report Climate Change and Land


  • Land surface air temperature has risen nearly twice as much as the global average temperature
  • Climate change, including increases in frequency and intensity of extremes, has adversely impacted food security
  • Climate change creates additional stresses on land, exacerbating existing risks to livelihoods, biodiversity, human and ecosystem health, infrastructure, and food systems
  • Not all regions will be affected in the same way
  • Changes in land conditions, either from land-use or climate change, affect global and regional climate

Read the full report here

Further reading

World Bank Turn Down the Heat Series

NASA Global Climate Change Website

World Metereological Organisation Climate Website

Munich RE Risks > Climate Change

Climate models – no crystal ball, but a solid foundation for decisions

We can measure actual temperatures and observe impacts of current levels of global warming – but we can’t look into the future, can we?

“If we had observations of the future, we obviously would trust them more than models, but unfortunately… observations of the future are not available at this time” –Tom Knutson and Robert Tuleya

To understand what is likely to happen, scientists have started to create climate models more than a century ago. Since then, thousands of scientists have worked to improve these models. Nevertheless, as the systems are immensely complex, some uncertainty remains. This is often used to question the overall findings. Watch Gavin Schmidt explain how climate models work and why they provide compelling evidence for action.

Climate sceptics, agnostics and deniers

People who do not accept the findings of climate science are often referred to as “climate sceptics” or “climate deniers.” Even though it is a small number within the scientific community, they have had significant influence on public opinion and in political discussions on the appropriate reaction to the scientific evidence.

Understanding the motivations is important to better address arguments made against evidence. The Conversation took a closer look at different forms of non-acceptance. Read the full article here.

They distinguish three categories:


Those who engage in scholarly disagreement through the literature.



Those who are not engaged with the debate and have no clear view either way.



Those who associate climate science with conspiracy, wilful ignorance or incompetence (or even see in it an unpalatable truth). Here they further distinguish:

  • ‘Naïve’ deniers, convinced of the incompetence of scientists and having a naïve view of their own analytical powers.
  • ‘Conspiracists,’ rejecting climate science because of its implications for social or economic change, who consequently see climate science as a conspiracy of social or political engineering.
  • ‘Opportunists,’ who accept climate science, but do not care about the consequences and seek to maximise their opportunities in any resulting crisis.


A useful website that looks at ‘climate myths’ regularly used by sceptics and deniers and explains the actual science behind those ‘myths’ is https://skepticalscience.com/

So why act…


Watch some compelling arguments why uncertainty in climate models shouldn’t prevent us from taking immediate and bold action:

Frequently asked questions

Do scientists agree on climate change?

Yes, the vast majority of actively publishing climate scientists agree that humans are causing global warming and climate change. A number of so-called ‘consensus’ studies analysed published articles on climate change and found an overwhelming agreement on human-caused global warming. Depending on the methodology used, they come to the conclusion that between 91% and 100% of scientists agree that climate change is happening and humans are responsible. Read more on studies conducted between 2004 and 2015 here and the latest study from 2017 here.

What is the greenhouse effect?

The greenhouse effect is the way in which heat is trapped close to the surface of the Earth by “greenhouse gases.” These heat-trapping gases can be thought of as a blanket wrapped around the Earth, which keeps it toastier than it would be without them. Greenhouse gases include carbon dioxide, methane and nitrous oxides.

Greenhouse gases arise naturally, and are part of the make-up of our atmosphere. Earth is sometimes called the “Goldilocks” planet – it’s not too hot, not too cold, and the conditions are just right to allow life, including us, to flourish. Part of what makes Earth so amenable is the naturally-arising greenhouse effect, which keeps the planet at a friendly 15 °C (59 °F) on average. But in the last century or so, humans have been interfering with the energy balance of the planet, mainly through the burning of fossil fuels that give off additional carbon dioxide into the air. The level of carbon dioxide in Earth’s atmosphere has been rising consistently for decades and traps extra heat near the surface of the Earth, causing temperatures to rise.

Source: NASA

How do we know what greenhouse gas and temperature levels were in the distant past?

Ice cores are scientists’ best source for historical climate data. Other tools for learning about Earth’s ancient atmosphere include growth rings in trees, which keep a rough record of each growing season’s temperature, moisture and cloudiness going back about 2,000 years. Corals also form growth rings that provide information about temperature and nutrients in the tropical ocean. Other proxies, such as benthic cores, extend our knowledge of past climate back about a billion years into the past. Read more here.

Why is 1880 often used as reference for global warming?

Three of the world’s most complete temperature tracking records – from NASA’s Goddard Institute for Space Studies, the National Oceanic and Atmospheric Administration’s National Climactic Data Center and the UK Meteorological Office’s Hadley Centre – begin in 1880. Prior to 1880, temperature measurements were made with instruments like thermometers. The oldest continuous temperature record is the Central England Temperature Data Series, which began in 1659, and the Hadley Centre has some measurements beginning in 1850, but there are too few data before 1880 for scientists to estimate average temperatures for the entire planet. Data from earlier years is reconstructed from proxy records like tree rings, pollen counts and ice cores. Because these are different kinds of data, scientists generally don’t put proxy-based estimates on the same charts as the “instrumental record.”

The above-mentioned agencies and others collect temperature data from thousands of weather stations worldwide, including over the ocean, in Antarctica and from satellites. However, instruments are not perfectly distributed around the globe, and some measurement sites have been deforested or urbanized since 1880, affecting temperatures nearby. Each agency uses algorithms to filter the effects of these changes out of the temperature record and interpolate where data is sparse, like over the vast southern ocean, when calculating global averages. Generally, all three datasets agree quite closely (see graph above) and are in agreement on the trend of global warming since the Industrial Revolution.

Source: NASA

What do volcanoes have to do with climate change?

Overall, volcanoes release less than 2 percent of the equivalent amount of CO2 released by human activities. Quite small. However, about once every 20 years there is a volcanic eruption (e.g., Mount Pinatubo, El Chichon) that throws out a tremendous amount of particles and other gases. These will effectively shield us enough from the Sun to lead to a period of global cooling. The particles and gases typically dissipate after about 2 years, but the effect is nearly global.

Source: NASA