This document provides an introduction to climate change science. It discusses that climate change is a large multi-disciplinary issue that affects all sectors of society and the economy. It then summarizes the key components of the climate system and how human activities have changed the composition of the air and land use. The document reviews evidence of climate change from increasing greenhouse gas concentrations and global temperature rise. It discusses climate modeling and projections for further warming and impacts. The conclusion emphasizes that human influence on climate is clear and emissions reductions are needed to limit climate change risks.

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

2. Climate Change is a Large Issue
Majority of the sciences are involved.
Business/Industry has a stake.
Involves citizens, politicians, public policy experts.
Every sector of the economy affected.
All aspects of our lives touched:
environment, jobs, health, politics, etc.

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

4. IPCC Assessment Reports since 1990: WGI Contribution
1990
1995
2001
2007
2013

5. 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

6. 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.

8. Primary energy consumption and total global
emissions are increasing

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

10. –18°C +15°C
Earth without air Our planet
+ 33°C
If the EARTH had no atmosphere, it would
be very cold

11. Natural GHG effect
33 °C
Other GHG <1 °C
CO2 2 °C
H2O 31 °C
–18oC
+15oC

12. Enhanced GHG
effect
33 °C
+ 1 °C
Other GHG <1 °C
CO2 2 °C + 1oC
H2O 31 °C
–18oC
+16oC

14. 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

15. Changes in water cycle
drier wetter

17. Number of world natural catastrophes
1980-2017

19. GHG radiative forcing values are
getting bigger every year

20. 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

21. 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. 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.

24. Regional aspects of surface warming
Knutti et al, Nat. Geo., 2015
1.5°C 2°C 4°C
°C

25. Regional aspects of precipitation change
Water cycle change :
• for 50% of world’s population at
+2°C
• for 40% of land surface at +3°C
Sedlacek and Knutti, 2014; Knutti et al, Nat. Geo., 2015
1.5°C 2°C 4°C
% precipitation
change

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

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

29. IPCC AR5 Synthesis Report
Impacts are already underway
• Tropics to the poles
• On all continents and in the ocean
• Affecting rich and poor countries
(but the poor are more vulnerable
everywhere)
AR5 WGII SPM

30. 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.

31. 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.