The science of climate change: What do we know about the greatest challenge that humanity is facing?

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Climate change is a reality. Scientific evidence shows that its effects, which are already occurring at an unprecedented rate, could be disastrous for the planet in the coming decades. Iberdrola has prepared a document (Science of Climate Change 2020. Present and Future) which brings together scientific information to make it easier to understand this global problem.

An analysis of the evolution of a series of indicators provides evidence on the changes that are occurring now and those that are foreseen in the future. For this reason, Iberdrola has prepared a document (Science of Climate Change 2020. Present and Future), which brings together leading scientific information in order to present an overview of the phenomenon of climate change. Its aim is to strengthen understanding of this global problem and its implications, while providing up-to-date data and information that may be useful in addressing its main risks.

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This document is part of our initiative to make educational materials available to society with the aim of raising awareness and training on climate change. Discover more materials to continue delving into this global challenge in our section 'Learn about climate change'.


For several decades now the climate has been changing at an unprecedented rate and scientific evidence points to human behavior as being responsible. The emission of greenhouse gases (GHG) that accumulate in the atmosphere and retain heat (greenhouse effect) contributes to an increase in the temperature of the planet. This change, which has an anthropogenic origin, is known as climate change and the science of climate change is therefore the study of the causes and effects of this phenomenon.

Definition of climate change. 
United Nations Framework Convention on Climate Change (UNFCCC)

Climate change means a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods


Climate change is a global phenomenon, it is occurring at high speed and will have long-term effects, which are already a reality. "Climate change is the defining challenge of our time," according to the United Nations Secretary-General, António Guterres. He also warns that it is an unprecedented threat to peace, prosperity and the Sustainable Development Goals (SDG). The scientific evidence is clear and below we will look at some of it:

 Human activities and emissions are affecting the composition of the atmosphere.

 The growing concentration of GHG in the atmosphere is contributing to an increase in the greenhouse effect and, consequently, global temperatures.

 The warming seen on the surface is related to other changes in the earth system — the deoxygenation of the oceans, retreating ice sheets (glaciers, for example), rising sea levels, an increase in extreme weather events, etc. —.

 The consequences of these changes are obvious in many different areas: biodiversity, health, food safety and water scarcity, poverty, conflicts and migration, and the economy.


1. The human influence on the climate system is clear

The additional emission of anthropogenic GHGs leads to an increase in the temperature of the planet with effects that can last for millennia before natural processes eliminate them from the atmosphere. The concentration of atmospheric CO2, the GHG that contributes more than 2/3 to global warming, reached its highest annual average of 409.8 ppm in 2019, levels higher than those observed for at least the last 800,000 years and well above the levels with which humans have coexisted.

The Intergovernmental Panel on Climate Change (IPCC) concluded that human influence through GHG emissions has been the main cause of the warming observed since the mid-20th century. The IPCC also considers that the goals of the Paris Agreement involve not exceeding a concentration of atmospheric CO2-eq of 450 ppm in order to limit the increase in temperature to 2 ºC, or 430 ppm for 1.5 ºC at the end of the century. The increase in the concentration of CO2 is mainly dueto emissions from burning fossil fuels, which account for three quarters of total CO2.

2. Scientific evidence shows that climate change is a reality

Scientific evidence shows that the effects of climate change are occurring at an unprecedented rate:

  • Global temperatures have increased systematically since 1880. Proof of this is the fact that 19 out of the 20 hottest years since records began have occurred since 2001. Specifically, 2019 was the second hottest year with an average surface temperature ~1.1 ºC higher than the preindustrial period (1850-1900). Since the 1980s, each decade has been warmer than the previous one, by intervals of 0.1 ºC to 0.3 ºC (World Meteorological Organisation, WMO).
  • The consequences of global warming can also be seen in other variables, such as shrinking ice sheets, the acidification and deoxygenation of the oceans and rising sea levels.
  • There is also a relationship between global warming and extreme weather events. In spite of the complexity of studying them, since by definition they are rare or exceptional, there is a general consensus that the its frequency and intensity are increasing in many regions as a result of global climate change.

3. Climate change is greatly affecting human well-being and all sectors of activity

Climate change and in particular extreme weather events affect human welfare and all sectors of activity, both directly and indirectly, because of their impact on natural ecosystems and socio-economic systems. Today, it is considered that this phenomenon is one of the three major drivers of the loss of biodiversity and that it is lowering the quality of the natural resources that are essential for the food supply. It was defined by the World health Organization in 2018 as the major challenge to health in the 21st century and one of the major threats to economic stability by a variety of international bodies.

4. Climate change will require adaptation actions

Adapting to climate change will be essential in coming decades, since there is a certain degree of change in the climate that is inevitable:

  • Because of accumulated emissions, the inertia of the climate system and current levels of emissions, the physical effects of climate change are similar in all short-term emissions scenarios to 2050 and it is foreseeable that the limit of 1.5 ºC will be reached around 2040 (IPCC) if current rates of warming continue.
  • The great variation in the physical results, always dependent on the actions of the coming decades, increases after 2050. Therefore, if global climate neutrality is reached by 2050, global temperatures could remain at +1.5 ºC by 2100. But stabilising the global surface temperature does not mean that all aspects of the climate system will be stabilised. For example, the sea level will continue to rise for centuries since it responds to changes more slowly.

5. Mitigation of climate change is vital

The greater the disturbance of the climate, the greater the risk of suffering generalised, severe and irreversible effects on ecological and human systems. To prevent these effects from increasing exponentially, every tenth of a degree of temperature rise avoided through mitigation actions is important. Limiting the temperature increase to 1.5 ºC by 2100 is still possible and it will make it possible to substantially reduce the seriousness of many of these effects — rise in sea level, cyclones, increasing fires, heat waves, typhoons, etc. —. This requires reducing emissions by 45 % by 2030 compared to 2010 and achieving net zero emissions by 2050.

6. Climate action will have a profound impact on the global climate

Worldwide efforts to reduce emissions in the coming decades will have a great impact on the global climate during the second half of this century. To do this, mitigation actions must be accompanied by actions to adapt to the changing conditions in order to effectively tackle the challenge of climate change.

Science of Climate Change 2020. Present and Future.#RRSSScience of Climate Change 2020. Present and Future.

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