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What's happening?

Before we can talk about climate action, it is important to understand and know what is going on with our climate. In this first part, we will talk about the Earth's climate, how it is changing, and what humans had to do with it. 


What is the difference between the climate and the weather?

These two terms are often confused resulting in statements such as: how can a scientist predict the climate in 50 years, when they cannot even predict the weather next week?


The weather is determined by whatever is happening in the atmosphere at a given time. This includes the temperature, the wind, the humidity etc. These characteristics change often and quickly so they are difficult to predict. Climate, on the other hand, is the average weather over longer periods ( often 30 years). Changes in climate are more likely to happen because of a change in the characteristics of the atmosphere itself. Since these changes are not chaotic, they are much easier to predict.


Reference: IPCC (2007): Frequently Asked Questions - What is the Relationship between Climate Change and Weather?

What makes up the climate system?

The Atmosphere: the envelope of gas surrounding the Earth

The Hydrosphere: all the liquid water on the surface and underground (lakes, rivers, oceans)

The Cryosphere: all the frozen water (snow, ice, glaciers)

The Lithosphere: all the solid Earth on land and oceans that feed into volcanic activity 

The Biosphere: all the living organisms and ecosystems on land and in the oceans (trees, animals)

What is the Greenhouse Effect?

The Greenhouse Effect is a term used in climate science to explain how the Earth is heating up. In agriculture, a greenhouse is a glass building where vegetables and flowers are grown and protected from harsh weather. The walls as well as the roof is made of glass so that sun rays can shine through. During the day, the sun shines heating up the plants. The heat is captured inside the building so that the inside stays relatively warm, even at night. 

Our Earth and atmosphere can be compared to a greenhouse. The Earth's surface acts as the plants growing inside and the atmosphere acts as the glass walls and roof. The sun shines at the Earth so that the flora and fauna can live and grow. Some of the sun shine is absorbed and some is reflected back up into the atmosphere. Then once more, some is absorbed and some is reflected into space or back to the Earth's surface. So everytime the Sun shines at the Earth, we "feel" it more than once. If we didn't have the atmosphere acting as the glass in a greenhouse, we would feel a global average temperature of -19 degrees, instead of our current 14 degrees.


The better the atmosphere is at reflecting back to the Earth's surface, the more we heat up. Some particles, known as greenhouse gases, enhance the atmosphere's ability to reflect back to the surface. If more of these gases are present in the atmosphere, the Earth will heat up more. Carbon Dioxide is a common greenhouse gas and is commonly emitted into the atmosphere by humans. Water vapour on the other hand is a greenhouse gas that is not influenced by humans. 

There are two types of greenhouse effects:
1. The natural greenhouse effect, which heats up the Earth's surface from -19 degrees to +14 degrees, allowing life to exist on Earth

2. The enhanced greenhouse effect, due to more greenhouse gases (CO2), which causes the Earth to heat up more than +14 degrees

What gases are in the atmosphere?

The two most present gases are Nitrogen (98%) and Oxygen (21%). They do not really add to the greenhouse effect mentioned above. Instead less common and more complex gases such as water vapour (no.1 greenhouse gas) and carbon dioxide (no. 2 greenhouse gas) play a big role in heating the Earth. Gases such as Methane, Nitrous Oxide and Ozone are only present in small amounts but contribute to the greenhouse effect. 

Reference: WMO, embed NASA video, IPCC (2007): Frequently Asked Questions - What is the Greenhouse Effect?

What are climate forcings?

Climate forcings is a term used to describe factors than change (or force) the climate system. The factors are often energetic and describe changes in energy in (more heat towards the Earth) or energy out (more heat out of the Earth). 

The most important climate forcings include:

- Changes in how much the sun shines

- Volcanos that erupt

- More greenhouse gases in the atmosphere (CO2)

Reference: IPCC (2013). Climate Change 2013: The Physical Science Basis - Summary for policymakers, p. 11

What are the effects of climate forcings?

Embed graph and explain the three mentioned above

Are there natural climate fluctuations?

Yes, there are also natural climate fluctuations that have a big impact on a local and global scale. One example is El Nino, La Nina and the El Nino Southern Oscillation (ENSO). 

This is a climate fluctuation pattern that occurs roughly every 5 years across the Pacific Ocean. El Nino refers to the ocean's surface getting hotter for 3 or more seasons. La Nina refers to the same ocean's surface switching back and getting colder than normal.

Reference: WMO website (embed imaged)

What's the difference between climate change and global warming?

Global warming refers to the overal warming of planet Earth. This is the average temperature over the entire surface of the Earth. Already since early 1900, scientists noticed this change in our climate that cannot have been due to natural effects from the past. It is also the fastest change ever to have been recorded by humankind.

Climate change refers to changes in climate characteristics over long time periods. These can include temperature, but also humidity, rainfall, wind and severe weather events. Global warming leads to other effects in the climate system; the combined effects are called anthropogenic or human-caused climate change.

Reference: WMO website

How much has the Earth's temperature changed?

The illustration below shows how much hotter different parts of the world have become since 1901. Almost the entire globe has experienced surface warming. In general, the average global surface temperature has increased by 0.85 degrees between 1880 - 2012.

Reference: IPCC (2013). Climate Change 2013: The Physical Science Basis - Summary for Policymakers, p3

Climate change affects more than just the environment

Climate change negatively impacts ecosystems (biodiversity, habitats), human systems (agriculture, fresh water, health), urban systems (transport, buildings, lifestyle), economic systems (energy, manufacturing, natural capital industries) and social systems (equity, migration, peace and conflict). 

We know we will be challenged in each of these ways, however we have difficulty determining to what extent. Climate change science allows us to understand how the climate is changing, how much of it is in our circle of influence and how we can expect it to change in the future. This will allow us to prepare for difficult times ahead by making the right decisions now in the way we govern our world and we act as humans on Earth.

In the short term, we can plan for weather events and prepare for possible emergencies. More extensive limate models help us forecast future scenarios. These scenarios show us what our world will look like and help us assess how we must adapt.

How long have we known about climate change?

Schematic of the history 

Unlike we might expext, climate change science has existed or a very long time. Already in 1824,  Joseph Fourier, a French physicist, first described the natural greenhouse effect. Irish physicst John Tyndall first showed in 1861 the connection between CO2 and H2O and the climate. Even before the 20th century, Swedish chemist Svante Arrhenius concluded the negative effect of industrial-age coal burning. 

The human part of climate change

The increased amount of greenhouse gases in the atmosphere comes from human activity. This is often referred to as "anthropogenic". 

Embed video of IPPC on the human influence on the climate system.

How dangerous are the various greenhouse gases?

Insert schematic of different greenhouse gases 

There are different types of greenhouse gases. They each have a different capacity to trap heat; this is called the "global warming potential (GWP)".  CO2 is the baseline unit to which all other greenhouse gases are compared. While CO2 has a GWP or 1, while the GWP of CH4 is 25. This means that in the same timespan, methane will trap 25 times more heat than CO2.


The schematic shows the seven most important ones that we emit into the atmosphere. Since they are all chemical stable, they remain in the atmosphere for very long times and thus can impact the climate for a very long time. Whilst the top three (CO2, CH4, N2O) exist naturally as well, the bottom 4 are only in the atmosphere because we put them there. 

Ref: IPCC (2007). Fourth Assessment Report, Technical Summary – Changes in Human and Natural Drivers of Climate UNEP (2012). Emissions Gap Report

Why is CO2 the most important greenhouse gas?

CO2, or carbondioxide, accounts for approximately 64% of the total effect. Rather than remaining in the atmosphere forever, CO2 cycles between the atmosphere, oceans and land biosphere. It is emitted primarily as a result of burning fossil fuels, deforestation

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