Quaternary Lecture 6- The Holocene epoch and global warming Flashcards
What are important highlights of the holocene?
- glacial/interglacial transition
- period of high precision palaeoclimatic reconstruction
- human impact on climate
When is the end of the Pleistocene?
MIS boundary 2/1
What are features of the end of the Pleistocene?
- ‘Late-glacial’ = 15-11.5 ka:
– Bølling/Allerød Interstadial 15-13 ka (‘Late-glacial Interstadial’)
– Younger Dryas Stadial 13-11.5 ka (‘Loch Lomond Stadial’
What does MAAt stand for?
Mean annual air temperature
What is the onset of the holocene marked by?
- Onset of Holocene marked by a rapid
increase in temp. - Ice core records suggest that MAAT increased by 7oC in 50 yrs
Discuss the early holocene thermal maximum.
Thermal optimum, hypsithermal - 9-5ka.
- Warmer than present in many regions by 1-2oC.
– Most intense at the Poles (Renssen et al., 2012). Disappearance of polar ice shelves.
– Northward expansion of deciduous woodland reaching max range limits by 6 ka.
The 8.2, 4.2 and 2.5 ka event
The Neoglacial, the Medieval Warm Period, The
Little Ice Age
What is the neoglacial?
- The HTM was followed by the late Holocene Neoglacial –climatic deterioration 4.5 – 2.5ka. Clear evidence across the N Hemisphere.
- The Neoglacial culiminated in the LIA.
- For example, evidence from Greenland for ice sheet re-growth, isostatic depression,
sea-level rise, ice shelf regrowth (Smith et al. 2023)
What is the little climatic optimum/ medieval warm period?
750-1200 AD
Period of historical observations
- Increase in temperatures (1-2oC)
- Warmest 800-1200 AD – but varies spatially & may not be global
- Reduced sea ice extent led to Viking settlement of Greenland c. 800-1000 AD
- Failure of Greenland Viking colonies by mid-1300s.
- Vineyards in S. Britain as recorded in the ‘Doomsday Book’ (AD 1086)
What is the little ice age?
1500-1900 AD
* Expansion of glaciers
* Southward migration of Arctic
sea ice
* Temperatures cooled 1-2°C
* Peaked c. AD 1700, but persisted
to 1900
* Thames Frost Fairs
Has there been more than one LIA?
Potentiall
LIATE (little ice age type events)
‘Little Ice Age’ glacierization occurred over about 650 years ago and can be defined most precisely in the European Alps (c. AD 1300–1950) when extended glaciers were larger than before or since
Little Ice Age’ climate is defined as a shorter time interval of about 330 years ( C . AD 1570–1900) when Northern Hemisphere summer temperatures (land areas north of 20°N) fell significantly below the AD1961–1990 mean.
How much has global average temp increased from 1850-2005?
0.9C
How much has global sea level rised between 1850-2005?
20cm
Discuss co2 levels between 1850 to now.
280-390ppm 1850-2005
Now 424ppm
40 GtCO2/yr
When did IPCC start monitoring CO2?
1990
What is the greenhouse effect?
Ability of atmosphere to retain or absorb energy (radiation) & re-radiate it (via CO2, CH4 & water vapour
What is driving GHG emissions?
Human-induced climate change indicators
i) Air pollution has increased atmospheric CO2
(~30%) since 1800’s
+ population growth, urbanization, agriculture
increase in other greenhouse gases CH4 &
N2O
ii) anthropogenic release of CO2
(fossil fuel burning & industry)
iii) reduction in forestry
less efficient recycling of CO2 by
photosynthesis
iv) CO2 increase mirrors global economic
growth
* Greenhouse gas concentrations have
increased to levels unprecedented in 800 kyr
* Human-induced runaway greenhouse effect
The Anthropocene
Have the last 10 years been the warmest on record?
Yes
What are GCMs?
Global circulation models - prediction of future climate.
Many model scenarios suggest a 2-3oC increase in global temp over the next
100 yrs. x10 faster than the warming of last 10 ka.
Are we heading towards a ‘RCP 8.5 world’ ? The worst projections possible.
Ganopolski et al (2016)
The past rapid growth of N Hemisphere ice sheets is generally attributed to reduced
summer insolation (governed by Milankovitch forcing). Yet such summer insolation is
near to its minimum at present, and yet there are no signs of a new ice age. - Why not?
* Ganopolski et al. propose a critical functional relationship between boreal summer
insolation and CO2 concentration, which explains the beginning of the past eight glacial
cycles.
* Ganopolski et al. suggest that glacial
inception was narrowly missed before the
beginning of the Industrial Revolution due
to high late-Holocene CO2 concentrations
and low orbital eccentricity of the Earth.
* Under natural future forcing the current
interglacial would probably last for another
50,000 years.
Talento and Ganopolski (2011)
- The beginning of the next glaciation is highly unlikely in the next 120 kyr.
- High cumulative anthropogenic CO2 will cause ice-free conditions in the N Hemisphere
throughout the next half a million years, postponing glacial inception up to 600 kyr after
present or later.
Clark et al (2016)
- Future climate warming = melt of the ice sheets and future sea-level rise
- Clark et al. Predict total the almost total loss of the Antarctic and Greenland ice
sheets - Long-term global mean sea-level projections for the next 10,000 years for four
emission scenarios (Clark et al., 2016) - Between 20-50m of global sea-level rise…………!!!!
Bradshaw et al (2021)
Human destruction of the planet
Firstly, the scale of the threats to the biosphere
and all its lifeforms—including humanity—is so
great that it is difficult to grasp for even well-
informed experts.
Second, what political or economic system, or
leadership, is prepared to handle the predicted
disasters, or even capable of such action.
Third, this dire situation places an extraordinary
responsibility on scientists to speak out when
engaging with government, business, and the
public.
The future stresses to human health, wealth and
well-being will perversely diminish our political
capacity to mitigate the erosion of ecosystem
services on which society depends.
The science underlying these issues is strong, but
awareness is weak. Without fully appreciating and
broadcasting the scale of the problems and the
enormity of the solutions required, society will fail
to achieve even modest sustainability goals
