Global Change_Lecture 1 16.02.2021
CLIMATE CHANGE: THE PHYSICAL SCIENCE BASIS
The lectures will be more about climate change, because of course climate change is an important component
of global change.
CONTENTS
1 Overview of the lecture ................................................................................................................................. 3
2 Some basics of the climate system ................................................................................................................ 3
2.1 The difference between weather and climate...................................................................................... 3
3 Changes in human and natural drivers of climate ......................................................................................... 4
3.1 Interactions are crucial to better understand the climate system. ...................................................... 4
3.2 The earth's climate system ................................................................................................................... 4
3.3 Radiation balance of the earth ............................................................................................................. 4
3.4 Calculation of the global mean temperature ........................................................................................ 4
3.5 The greenhouse effect .......................................................................................................................... 5
3.6 Absorption spectra of greenhouse gases in the near infrared ............................................................. 5
3.7 Greenhouse gases in the atmosphere .................................................................................................. 6
3.8 Water vapour is a feedback, not a forcing ............................................................................................ 6
3.9 Greenhouse effect: effect of doubling the CO2 concentration. ........................................................... 6
4 Observation of changes in climate ................................................................................................................ 7
4.1 Changes of the atmospheric concentrations of carbon dioxide, methane and nitrogen oxide over the
last 2000 years.................................................................................................................................................... 7
4.2 Detailed measurements on Hawaii since 1958. .................................................................................... 7
4.3 Concentration of greenhouse gases from Antarctic ice cores .............................................................. 7
4.4 The increasing CO2 concentrations in the atmosphere arise primarily from the combustion of fossil
fuels. 7
4.5 Fate of anthropogenic CO2 emissions (2009-2018 average) ................................................................ 8
4.6 Role of aerosols (suspended particles in the air) .................................................................................. 8
4.7 Radiative forcing of the climate (1750-2011) ....................................................................................... 8
4.8 Share of human activities to the enhanced greenhouse effect ............................................................ 9
5 Attribution of climate change ...................................................................................................................... 10
5.1 Rise of global mean surface temperature........................................................................................... 10
5.2 Mean annual temperature rise in Brussels 1833 - 2019. .................................................................... 10
5.3 Observed widespread warming .......................................................................................................... 10
5.4 Cause of the warming (attribution) .................................................................................................... 10
6 Impacts of climate change on the cryosphere and sea level ....................................................................... 12
6.1 Components of the cryosphere .......................................................................................................... 12
6.2 Decrease of seasonal snow cover ....................................................................................................... 12
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6.3 Less river and lake ice ......................................................................................................................... 13
6.4 Decline of Artic sea ice ........................................................................................................................ 13
6.5 2012 extent was lowest summer record so far .................................................................................. 13
6.6 Mountain glaciers ............................................................................................................................... 13
6.7 Worldwide glacier retreat since 1850. ................................................................................................ 13
6.8 The polar ice sheets have the largest potential for sea-level rise....................................................... 13
6.9 Recent evolution of the Greenland ice sheet ..................................................................................... 14
6.10 Evolution of the greenland ice sheet: 1990 to 2012 ........................................................................... 14
6.11 Recent evolution of the Antarctic ice sheet ........................................................................................ 14
6.12 Global average sea level change ......................................................................................................... 14
6.13 Land ice 2007-2016 ............................................................................................................................. 15
7 Projections of future climate change .......................................................................................................... 15
7.1 Climate projections ............................................................................................................................. 15
7.2 Equivalent CO2 concentration and emissions in the various scenarios .............................................. 15
7.3 IPCC AR5 projections of global mean temperature ............................................................................ 16
7.4 Temperature projections for the end of the 21th century ................................................................. 16
7.5 Projection of future precipitation change........................................................................................... 16
7.6 Climate projections for Europe in 2100 .............................................................................................. 16
7.7 IPCC SROCC projections of global sea level rise .................................................................................. 17
7.8 The longer-term poison: the long life time of atmospheric CO2 and the inertia if the climate system
17
7.9 Climate changes are effectively irreversible for more then 1000 years after emissions stop. ........... 17
7.10 Commitment to sea level rise ............................................................................................................. 18
7.11 Land below sea level today +1m + 8m ............................................................................................... 18
7.12 Cumulative carbon determines warming ........................................................................................... 18
7.13 Warming caused by cumulative carbon emissions to 2010. ............................................................... 18
8 Limiting climate change ............................................................................................................................... 19
8.1 Agreement in Paris.............................................................................................................................. 19
8.2 IPCC SR1.5 (2018) update of the carbon budget ................................................................................ 19
8.3 Emissions must decline rapidly ........................................................................................................... 20
8.4 Global fossil CO2 emissions including 2020 ........................................................................................ 20
8.5 To keep temperatures below 2degrees requires 2/3 of fossil fuels to remain in the ground ............ 20
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1 OVERVIEW OF THE LECTURE
Today is to illustrate you on the physical signs of climate change. I am going to explain some basics of the planet
system from a physical point of view, then I'll go on with some key components in the Climate System, the
changes in human and natural drivers of the climate. Then i will particular emphasis on the atmosphere. I will
explain why climate change is man-made, that's come attribution of climate change, I will also explain what is in
store for the future and what we need to do and what science tells us that we need to do to limit climate change
into the future.
2 SOME BASICS OF THE CLIMATE SYSTEM
2.1 THE DIFFERENCE BETWEEN WEATHER AND CLIMATE
Just one thing about the difference between weather and climate, because it is the first of a lot of
misunderstandings when we are talking about climate change. When we have a cold period or a cold week,
many people start thinking that its right what they are saying about climate change and global change. Other
people think; how can we predict climate change, if we cannot even predict next week's weather?
DIFFERENCE? They are two very different things; weather and climate. The weather is just looking at the
atmosphere of the Climate System and is nothing more than the momentary condition, than the condition of
the atmosphere at a given place.
WEATHER? You can measure the weather; air temperature, humidity and radiation and some other
components. Also, the weather cannot be predicted very far ahead, because there are so many components.
One of the reasons is that there are so many feedbacks and so many interactions in the atmosphere that when
you start a modelling and you change the initial conditions by a very small amount, you will get a very different
outcome after 10-14 days. This is something that is exemplified by 'the Lorenz butterfly'. If a butterfly flaps its
wings in the Amazon, it may cause a thunderstorm taking place somewhere else in 10 days ahead. If the butterfly
didn’t flap its wings, this may have not happened. This explains the fact that a small event can have a very big
impact in a different place sometime in the future.
CLIMATE? Climate is something different, it's looking at the averages of conditions over a longer period, mostly
over 30 years. We are looking at the mean and at extreme conditions.
CLIMATE IS THE STATISTIC OF THE WEATHER: So, it is mostly called the statistic of the weather. Statistics are
much easier to handle, they are much easier to predict. For example, it's generally possible to predict how the
life expectancy, how the average age of a population will evolve over time, we are likely to get older in the future
of course. But it is not possible to predict how old an individual person will become. This is the same with climate
and weather. Weather is just an individual component and climate is a statistic, these are much easier to handle.
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3 CHANGES IN HUMAN AND NATURAL DRIVERS OF CLIMATE
3.1 INTERACTIONS ARE CRUCIAL TO BETTER UNDERSTAND THE CLIMATE SYSTEM.
If you're looking at the climate, we are looking at interactions, details and scales become important. We are not
only looking at atmosphere, what is above us. We are also looking at the hydrosphere, which is everything with
water on the earth surface, like oceans. We are also looking at the cryosphere, that is all of the frozen water on
the earth's surface. We are also looking at the biosphere, which is all of the plans and then at the earth itself,
which is the lithosphere.
3.2 THE EARTH'S CLIMATE SYSTEM
This shows you the complexity of the Earth's Climate System, it is very complex system because of all the
different components, because of all the different interactions. Here we see single arrows but also double
arrows. The double arrows are interactions between different components, are the feedbacks between different
components. The single arrows are forcing, if these components change in one system that makes changes in
another system.
We start to understand the system better and better, also the models used to understand the system are getting
better and better. After all, the Climate System obeys simple physical laws, it is a physical system and obeys
simple physical rules, like the conservation of energy, the conservation of mass and the conservation of
momentum. It gets all its power, its energy from the sun.
3.3 RADIATION BALANCE OF THE EARTH
Talking about the conservation of energy, this very basic
physical conservation law also applies to the earth. We have a
global mean and an annual mean. The energy balance of the
Earth is also called the radiation balance.
INCOMING RADIATION = OUTGOING RADIATION: It must be
balance; what the Earth is receiving from the Sun which is the
incoming radiation must be balanced by the outgoing radiation.
3.4 CALCULATION OF THE GLOBAL MEAN TEMPERATURE
T is the only one we don't know, all the others we know. We can see how the global mean temperature depends
on the solar radiation, on Earth albedo and on the effective emissivity.
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