This document provides an introduction to climate change science. It discusses the components of the climate system and how human activities like burning fossil fuels and changing land use are rapidly increasing greenhouse gas concentrations and warming the planet. Climate models have improved and show continued warming in coming decades. The impacts of a changing climate include changes to water cycles, more extreme weather, and crossing dangerous climate thresholds. The options to address climate change are mitigation of emissions or adaptation to impacts, otherwise suffering the consequences of unabated climate change will result.

1. Introduction to climate change science
Prof. Lučka Kajfež Bogataj
University of Ljubljana, Slovenia

2. What is happening in the
climate system?
What are the risks?
What can be done?

3. Climate system
Main components: the atmosphere, hydrosphere [liquid water
components], cryosphere [frozen water components], lithosphere [land
surface] and biosphere [living things]) and the interactions between them

4. THE COMPOSITION OF AIR IS
CHANGING RAPIDLY due to human
activities:
→ more GHG (CO2, CH4, NOx...)
→ more aerosol (air pollution)
Human activities induced LAND USE
CHANGES
→ deforestation changed CO2 balance, more
GHG (CO2)
→ changes in albedo, water balance etc.

5. LIFESTYLE TODAY IS HIGLY ENERGY CONSUMING
One person
energy need
≈ 1GigaJ per day

6. Primary energy consumption and total global
emissions are increasing

7. 30%
11.0
GtCO2/yr
Fate of anthropogenic CO2 emissions
(2007–2016)
Source: Global Carbon Budget 2017
24%
8.8
GtCO2/yr
34.4
GtCO2/yr
88%
12%
4.8
GtCO2/yr
17.2
GtCO2/yr
46%
Sources = Sinks
6%
2.2 GtCO2/yr
Budget Imbalance:
(the difference between estimated sources & sinks)

8. The atmospheric concentrations of CO2, methane, and
nitrous oxide have increased to levels unprecedented in at
least the last 800,000 years.

11. Warming rate K/100 y
• The Earth gets warmer as CO2 increases in the atmosphere
• The Earth doesn't warm uniformly, the oceans warm slower
than the continents and arctic

12. Changes in water cycle
drier wetter

14. Number of world natural catastrophes
1980-2017

16. GHG radiative forcing values are
getting bigger every year

17. RCPs Scenarios
Representative Concentration Pathways
radiative forcing values in the year 2100 relative to pre-industrial values
+2.6, +4.5, +6.0, and +8.5 W/m2

18. Climate models
• Climate models are systems of differential
equations based on the basic laws of physics,
fluid motion, and chemistry.
• GCMs divide earth into many layers of grids.
GCMs provide forecasts for each grid point,
which represent average values for a grid.
• Using more than one GCM is recommended to
avoid the effects of model bias.

19. Climate models have improved in the last decade. Models
reproduce observed surface temperature patterns and trends
over many decades and are used for climate projections.

22. Downscaling is a technique to obtain information for a
finer scale from information for a larger scale.

23. Projections Europe (RCP4.5)
2081-2100 versus 1986-2005
Temperature (oC) Precipitation (%)
winter summer winter half summer half

24. Feedbacks are important to climate change
• They have the potential to radically affect climate change.
• There are both negative and positive feedbacks, the big
question is how these will balance out
• Some types of feedback are well understood by climate
scientists and their effects are included in climate models
(water vapour - positive feedback, albedo -positive
feedback)
• Some are less understood (land and ocean carbon cycle,
clouds)
• Some are not at all included in the models (permafrost
methane -positive feedback, methane hydrates - positive
feedback)

25. Dangerous climate thresholds
Evidence suggests the Earth’s climate has reached critical
thresholds in the past, triggering abrupt change. Climate
models suggest such thresholds could be reached again
as the Earth warms from increasing GHG emissions
• Arctic sea ice
• Changes in ocean circulation
• Permafrost
• Tropical and boreal forests
• Ice sheets
• Methane release from the seabed

26. Dangerous climate thresholds

27. Facing the dangers from climate change…
…there are only three options:
Mitigation, meaning measures to reduce the
pace & magnitude of the changes in global
climate being caused by human activities.
Adaptation, meaning measures to reduce the
adverse impacts on human well-being resulting
from the changes in climate that do occur.
Suffering the adverse impacts that are not
avoided by either mitigation or adaptation.

28. Concluding thoughts
• Human influence on the climate system is clear.
This is evident from the increasing GHG
concentrations, observed warming, and
understanding of the climate system.
• Continued emissions of GHG will cause further
warming and changes in all components of the
climate system.
• We can still limit climate change by substantial
and sustained reductions of greenhouse gas
emissions.