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Introduction to Climate Science
1. Outreach Event on the Role and Activities of the Intergovernmental Panel on
Climate Change (IPCC)
SUDAN KHARTOUM, 12 – 13 August 2018
Introduction to climate science
Fatima Driouech
Vice Chair IPCC WGI
2. Weather is the state of the atmosphere at a
particular time.
The climate represents the synthesis of weather
conditions in a given area, characterized by the
statistics of the meteorological elements in that
area over a long-term (decades and more).
Climate & weather
3. The interactions
and exchanges
between the
climate system
components
influence the
climate
Schematic view of the components of the climate
system, their processes and interactions. Source:
IPCC (2007): AR4
4. Climate change refers to a change in the state of the
climate that can be identified by changes in the mean
and/or the variability of its properties, and that
persists for an extended period, typically decades or
longer.
Climate change definition
The UN Framework Convention on Climate
Change (UNFCCC) defines climate change as: 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
6. • The temperature has
increased by 0.85°C over
1850 - 2012
• Warming of the climate
system is unequivocal
Top panel: annual mean values.
Bottom panel: decadal mean values.
Source: IPCC (2013): AR5
In the Northern
Hemisphere,
1983-2012 was the
warmest since 1400
years.
12. 1. FD, Number of frost days: Annual count of
days when TN (daily minimum temperature) <
0oC.
2. SU, Number of summer days: Annual count of
days when TX (daily maximum temperature) >
25oC.
3. ID, Number of icing days: Annual count of days
when TX (daily maximum temperature) < 0oC.
4. TR, Number of tropical nights: Annual count of
days when TN (daily minimum temperature) >
20oC.
5. GSL, Growing season length: Annual (1st Jan
to 31st Dec in Northern Hemisphere (NH), 1st July
to 30th June in Southern Hemisphere (SH)) count
between first span of at least 6 days with daily
mean temperature TG>5oC and first span after
July 1st (Jan 1st in SH) of 6 days with TG<5oC.
6. TXx, Monthly maximum value of daily
maximum temperature.
7. TNx, Monthly maximum value of daily minimum
temperature.
8. TXn, Monthly minimum value of daily maximum
temperature.
9. TNn, Monthly minimum value of daily minimum
temperature.
10. TN10p, Percentage of days when TN < 10th
percentile
11. TX10p, Percentage of days when TX < 10th
percentile
12. TN90p, Percentage of days when TN > 90th
percentile
13. TX90p, Percentage of days when TX > 90th
percentile
14. WSDI, Warm spell duration index: Annual
count of days with at least 6 consecutive days
when TX > 90th percentile
15. CSDI, Cold spell duration index: Annual count
of days with at least 6 consecutive days when TN
< 10th percentile
16. DTR, Daily temperature range: Monthly mean
difference between TX and TN
13. 8. TXn, Monthly minimum value of daily
maximum temperature.
9. TNn, Monthly minimum value of daily
minimum temperature.
10. TN10p, Percentage of days when TN <
10th percentile
11. TX10p, Percentage of days when TX <
10th percentile
12. TN90p, Percentage of days when TN >
90th percentile
13. TX90p, Percentage of days when TX >
90th percentile
14. WSDI, Warm spell duration index:
Annual count of days with at least 6
consecutive days when TX > 90th percentile
15. CSDI, Cold spell duration index: Annual
count of days with at least 6 consecutive
days when TN < 10th percentile
16. DTR, Daily temperature range: Monthly
mean difference between TX and TN
17. Rx1day, Monthly maximum 1-day precipitation
18. Rx5day, Monthly maximum consecutive 5-day
precipitation
19. SDII Simple pricipitation intensity index
20. R10mm Annual count of days when PRCP≥
10mm
21. R20mm Annual count of days when PRCP≥
20mm
22. Rnnmm Annual count of days when PRCP≥
nnmm, nn is a user defined threshold
23 CDD. Maximum length of dry spell, maximum
number of consecutive days with RR < 1mm
24 CWD. Maximum length of wet spell, maximum
number of consecutive days with RR ≥ 1mm
25. R95pTOT. Annual total PRCP when RR > 95p.
26. R99pTOT. Annual total PRCP when RR > 99p
27. PRCPTOT. Annual total precipitation in wet
days
14. Source: IPCC (2013)
- Precipitation in eastern Africa shows a high degree of temporal and spatial
variability (Rosell and Holmer, 2007; Hession and Moore, 2011).
- Over the last 3 decades rainfall has decreased over eastern Africa between March
and May/June (Williams and Funk (2011) and Funk et al. (2008).
17. Human influence on the climate system is clear,
and recent anthropogenic emissions of
greenhouse gases are the highest in history
18. Human influence has been detected in warming of the atmosphere and the
ocean, in changes in the global water cycle, in reductions in snow and ice, in
global mean sea level rise, and in changes in some climate extremes. This
evidence for human influence has grown since AR4. It is extremely likely that
human influence has been the dominant cause of the observed warming since
the mid-20th century.
19. Température mer plus élevée: vents +3.6 m/s, pluies +35%
Niveau mer +19 cm
Vents (avec température mer réelle) Vents (température mer «normale »)
Magnusson et al 2013 WMR
Ouragan Sandy (30 oct. 2012)
$ 70 billion damage around New York: winds, rains and submersion
20. Climate model is a numerical
representation of the climate
system that reproduces, with
as much fidelity as currently
feasible, the complex
interactions between the
atmosphere, ocean, land
surface, snow and ice, the
global ecosystem and a
variety of chemical and
biological processes.
Climate models
Schematic view of horizontal and vertical grids of a
climate model and of physical processes that it can
include. Source: NOAA
21. Climate models
Evaluations of the capabilities
and limitations of models is a
part of their process
development
Model capability in simulating annual mean
temperature and precipitation patterns. Source:
IPCC (2013):WGI-FAQ 9.1
27. Future changes of sea level rise
Global mean sea
level will continue
to rise during the
21st century.
28. Source: GIEC ( AR5)
Future changes of precipitation and evaporation
RCP 8.5: 2081-2100
29. Future changes of precipitation
Maps of precipitation changes in 2081–2100 with respect to 1986–2005 in the RCP8.5
scenario. For each point, the 25th, 50th and 75th percentiles of the distribution of the
CMIP5 ensemble are shown.
30. Contrasts between wet and dry regions will increase
Changes in the water cycle
for half of the world’s population in a 2°C
warmer world
over half of the land surface for a 3°C
warmer world
Sedlacek and Knutti, 2014; Knutti et al, Nat. Geo., 2015
32. The 1981–2000 time mean of the annual minimum of TN (TNn, top panel) and maximum of TX (TXx,
bottom panel) for HadEX2 and the CMIP5 multimodel ensemble median.
Sillmann et al.(2013) : Climate extremes indices in CMIP5
34. The 1981–2000 time means of the annual
R95p, RX5day and CDD for HadEX2 and the
CMIP5 multimodel ensemble median.
Sillmann et al.(2013) : Climate extremes
indices in CMIP5
35. Schleussner et al (2016a, 2016b)
Implications de 1.5 et 2° de réchauffement global
37. Achievements: 2013/2014 Fifth Assessment Report
Human influence on the climate system is clear
Key messages
The more we disrupt our climate, the more we risk severe, pervasive and irreversible impacts
We have the means to limit climate change and build a more prosperous, sustainable future
40. Sources of emissions
Energy production remains the primary driver of GHG emissions
35%
24% 21% 14%
6.4%
2010 GHG emissions
Energy Sector
Agriculture,
forests and
other land uses
Industry Transport
Building
Sector
AR5 WGIII SPM
41. The window for action is rapidly closing
72% of our carbon budget compatible with a 2°C goal already used
and continued emissions at current levels will exhaust the budget
within the next 15-30 years
Amount Used
1870-2016:
565
GtC
Amount
Remaining:
225
GtC
Total Carbon
Budget:
790
GtC
42. Influence humaine sur la composition atmosphériqu
IPCC AR5 WG1, 2013
Les teneurs en CO2, CH4 et N2O dans l’atmosphère ont atteint des niveaux
sans précédent depuis plus de 800,000 ans.
43. Ouragan Sandy (30 oct. 2012)
$ 70 billion damage around New York: winds, rains and submersion
Forecast (with actual SST) Forecast (with “normal” SST)
Magnusson et al 2013 WMR
44. Source: S. Planton (in http://education.meteofrance.fr)
RCP : Representative Concentartion Pathways
SRES : Special report on Emissions Scenarios
Évolution du bilan radiatif de la terre ou « forçage radiatif »
en W/m2 sur la période 1850-2250 selon les différents scénarios
45. Figure 1.13 | The development of
climate models over the last 35 years
showing how the different
components were coupled into
comprehensive climate models over
time. In each aspect (e.g., the
atmosphere, which comprises a
wide range of atmospheric
processes) the complexity and
range of processes has increased
over time (illustrated by growing
cylinders). Note that during the same
time the horizontal and vertical
resolution has increased
considerably e.g., for spectral
models from T21L9 (roughly 500 km
horizontal resolution and 9 vertical
levels) in the 1970s to T95L95
(roughly 100 km horizontal
resolution and 95 vertical levels) at
present, and that now ensembles
with at least three independent
experiments can be considered as
standard.
Notas do Editor
To understand climate and estimate its evolution and changes, the five components of the climate system should be considered:
These are:
the atmosphere: which is the envelope of gas surrounding the Earth
the hydrosphere: which contains the liquid water of the Earth’s surface and underground (e.g. oceans, rivers, lakes…)
the cryosphere: contains water in its frozen state (e.g. glaciers, snow, ice…)
the lithosphere: which is the upper layer of solid Earth on land and oceans supporting volcanic activity which influence climate
the biosphere: contains all the living organisms and ecosystems over the land and in the oceans
The figure, taken from the IPCC AR4, gives a schematic view of the processes and interactions linking climate system components. The interactions and exchanges of energy and matter between the climate system components influence the climate dynamics, its state and changes. For example:
the oceans store a great part of solar radiation; helps to distribute heat around the globe; absorb and store carbon dioxide and play an important role in the water cycle
ocean-atmosphere exchanges at the tropics explain an internal climate anomaly that occurs in the Pacific and that has global impacts for more than a year, the El Niño phenomenon. Click on the button for more information on El Nino
- Sea ice cover reduce the intensity of the heat coming from the ocean to warm the air.
A decrease in snow cover can lead to a decrease in surface albedo which in turn increases the absorbed solar radiation by the surface and leads to increased local air temperature.
- the forests influence climate by affecting the amount of carbon dioxide in the atmosphere. They remove carbon dioxide from the atmosphere and store it over long periods
- Changes in the biosphere through for example land use can influence surface albedo and then the reflected solar radiation amount by the earth surface
What is meant by climate change ?
Climate change refers to a change in the state of the climate that can be identified by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer.
To recall the link with weather: note that when we talk about climate change, we talk about changes in long-term averages of daily weather.
According to the Fifth Assessment report of the Intergovernmental Panel on Climate Change (the IPCC), multiple independent observations and climate indicators, from high up in the atmosphere to the depths of the oceans showed and evident warming of the world.
The warming is clearly visible in surface, atmospheric and oceanic temperatures.
The figure shows the raising trend of the globally averaged temperature for the period 1850 to 2012.
The temperature has increased by 0.85°C over this period.
It can be also noted that each of the three last decades of such period was warmer than all the precedents.
Note that the rate of warming was not uniform on time.
The years 1983 to 2012 represents probably the hottest 30-year period in the northern hemisphere in 1,400 years.
The Warming of the climate system is unequivocal
In terms of spatial distribution of surface temperature change, as showed by the figure on the left, almost the entire globe has experienced surface warming.
But this warming has regional contrast.
For example, mean temperature trends over the period 1901-2012 reached 1.5 to 2.5 °C in regions of north Africa, south America and northern Asia. The trends remained below 0.4°C in some parts of south-eastern North America.
Regional contrast of temperature change is also highlighted by both minimum and maximum temperatures as showed by the figures in the right representing the change between two recent periods: 1999-2018 and 1986-2005 using gridded high resolution CRU data.
As per the last few years, the WMO Statement on the State of the Global Climate reports, confirm that the last three years (2015, 2016 and 2017) are the warmest on record since 1850. They exceeded respectively the 1981–2010 average by 0.45°C, 0.56°C and 0.46 °C.
The warmest year in record is 2016, 2017 is the warmest among the non-El Nino ones. for information about the role of El Nino, see the video in the left down of this page
Note that :
according to the fifth IPCC Assessment Report :
Along with mean temperatures, both maximum and minimum temperatures have increased especially since 1950 (AR5 TS WGI)
Extreme temperatures have also changed compatibly with the warming trend: In fact a decrease in cold temperature extremes and an increase in
warm temperature extremes have been observed since about 1950 (AR5 SPM)
Glaciers, ice and snow have also registered several changes and the IPCC fifth Assessment Report confirms that:
The amounts of snow and ice have diminished. And Glaciers have continued to shrink almost worldwide.
Snow extend in the northern hemisphere has declined since the mid-20th century. Figure a in the top shows a clear decrease in northern hemisphere snow cover in spring season.
Figure b shows a clear decrease in the arctic summer sea ice extend.
AS reported in the last IPCC Working Group one technical summary, in most regions analyzed, it is likely that decreasing numbers of snowfall events are occurring where increased winter temperatures have been observed (TS WGI)
The duration of the NH snow season has declined by 5.3 days per decade since the 1972/1973 winter (TS WGI)
Precipitation patterns has also registered several changes
The figure shows observed change in annual precipitation over land for two periods: 1901-2010 in the left, and 1951-2010 in the right. Several regions has registered changes in the total amount of precipitation.
The spatial contrast of changes is clear and evolutions in opposite senses are visible:
for example Mediterranean region and west African, exhibits negative trends for the 1951-2010.
At the same time, most of European and north American regions registered an increase in annual precipitation amount.
It can also be easily noted that there is more regions with increasing trends than with a decrease.
According to the IPCC fifth assessment report, averaged precipitation over the mid-latitude land areas of the Northern Hemisphere has increased especially after 1951 (AR5 SPM)
Climate model is a numerical representation of the climate system that reproduces, with as much fidelity as currently feasible, the complex interactions between the atmosphere, ocean, land surface, snow and ice, the global ecosystem and a variety of chemical and biological processes.
Climate models are developed by scientists to understand and predict the climate system.
In order to be able to do this, the models divide the earth, ocean and atmosphere into a grid. The values of the predicted variables, such as surface pressure, wind, temperature, humidity and rainfall are calculated at each grid point over time, to predict their future values. IPCC (2013): WGI AR5
Each of the thousands of 3-dimensional grid cells can be represented by mathematical equations that describe the materials in it and the way energy moves through it. The advanced equations are based on the fundamental laws of physics, fluid motion, and chemistry. To "run" a model, scientists set the initial conditions (for instance, setting variables to represent the amount of greenhouse gases in the atmosphere) and have powerful computers solve the equations in each cell. Results from each grid cell are passed to neighboring cells, and the equations are solved again. Repeating the process through many time steps represents the passage of time. Source: https://www.climate.gov/file/atmosphericmodelschematicpng
The figure illustrates an example of grids and physical processes that can be included in a climate model.
The degree of complexity of models varies based on, for example, the extent to which physical, chemical or biological processes are explicitly represented.
Climate models vary also upon their spatial resolution which is the physical distance (in metres or degrees) between each point on the grid used to compute the equations.
Climate models have been developed and their representation of climate system processes and interactions improved over time. But to have confidence in the future projections they provide, historical climate—and its variability and change—must be well simulated.
Evaluations of the capabilities and limitations of models became a part of their process development
The Figure shows model capability in simulating annual mean temperature and precipitation patterns as illustrated by results of three phases of the Coupled Model Intercomparison Project (CMIP2, models from about year 2000; CMIP3, models from about 2005; and CMIP5, the current generation of models). The progress and the good ability of models are well illustrated.
Models have been demonstrated to reproduce observed features of recent climate and past climate changes
For example Models was skillful in reproducing the climate response to: solar cycle, orbital changes over the last 6000 years, or ice sheets 20000 years ago, 20th century multi decadal trends
In summary, confidence in models comes from their physical basis, and their skill in representing observed climate and past climate changes. Models have proven to be extremely important tools for simulating and understanding climate, and there is considerable confidence that they are able to provide credible quantitative estimates of future climate change.
Note however that climate models are not the exact reality by they ……………………..????????????????????????
