climate variability and global change Flashcards
why is solar forcing of climate especially topical?
Satellite instrumental quantification of solar influences Recent scientific advances
Geopolitics
Linkage between solar influence and regional climate (key for interannual to decadal-scale forecasting/ climate prediction)
what is geopolitics?
Climate change sceptics cite solar effects as cause of warming and/ or refer to “warmer” periods of the past – e.g. mediaeval warm period
when was climate first publicated?
1611- first scientific publication on sunsports. it took some 230 years before cyclic behaviour of sun spots was first documented by Heinrich Schwabe, an amateur
how are sunspots and climate joined?
A prolonged near- absence of sunspots 1645 – 1715 remarked on by contemporary astronomers – as were paucity of aurorae
Astronomers Spörer (1887) and Maunder (1890) drew attention to the minimum.
Coincidence of the “prolonged solar minimum” to the coldest excursion of the “Little Ice Age” was pointed out in the 1960’s and pulled together in a “seminal” paper in 1976
what did the prolonged solar minimum coincide with?
This coincided with the “great crisis” - unprecedented instability
During the 17th century
- Decreased agricultural production - European population decreased by 1/3 (Germany by ½) - Unprecedented numbers of wars (incl. 30 Years War 1618 - 48)
what are sunspots?
Magnetic field lines of sunspots suppress convection and stop plasma from sliding sideways into sunspot
Sunspots are temporary phenomena on the Sun’s photosphere that appear as spots darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. Sunspots usually appear in pairs of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.
what do sunspots look like?
appear as dark blotches on the Sun in which strong magnetic forces block the hot solar plasma (large-diameter magnetic flux tubes inhibit energy upflow) so sunspots are cooler and darker than their surroundings.
what is Faculae?
appear as bright blotches on surface of Sun, put out more radiation than normal and increase solar irradiance
how are faculae like sunspots?
Like sunspots, faculae are also the result of magnetic storms, but due to small-diameter magnetic flux tubes enhance energy upflow so T(faculae) ≈ 6200 K
how do faculae numbers increase and decrease?
Faculae numbers increase and decrease in concert with sunspots but are much more numerous than sunspots so the heating effects of the faculae exceed (x2) the cooling effects of the sunspots.
what does TSI stand for?
total solar irradiance
what is evidence of changing in irradiance?
Satellite measurements since 1978 show changes in total solar irradiance (TSI) through solar cycle only 0.1% BUT… UV radiation changes 6-8% short UV and X-ray double
Solar
wehre did the ozone changes take place when solar forcing of climate occurred?
2-4% in upper stratosphere
how did temperature change due to solar forcing of climate?
2 K range over solar cycle in tropical upper stratosphere
- propagates downwards to 2 K cooling at tropical stratopause at solar minimum
So at Solar Min – lower Stratosphere Equator – Pole Temp gradient is Δ 2 K less
how did drive circulation changes due to solar forcing of climate?
Reduced Equator – Pole T gradient – in N. Hem. Winter
- easterly wind anomaly – moves Nth – and weakens westerly Polar Vortex
is there evidence for sunspot forcing of climate at multi-year and decadal periods?
“We conclude that the 11-year cycle sometimes seen in climate proxy records is unlikely to be driven by solar forcing, and most likely reflects other natural cycles of the climate system ….
what are the proxies for solar activity- what other solar activity is there?
Sun spots are just one manifestation of increased solar activity that includes:
solar flares; mass coronal ejections and associated solar wind
how does solar wind increase?
Solar wind emitted from coronal holes on the sun carries magnetic fields which deflect galactic cosmic rays (GCR)
High solar activity causes strong solar wind emission causing a stronger deflection of galactic cosmic rays
so get decreased production of cosmogenic radionuclides
what does GCR stand for?
galactic cosmic rays
what are GCR?
GCR are mainly high energy particles e.g. protons, neutrons
Solar wind particles are mainly lower energy and mainly affect the upper atmosphere so do not generate the “cosmic” radionuclides 10Be, 14C etc
how has solar forcing changed on centernnial timescales?
longer term solar variability does influence climate
Do Solar Sunspot cycles influence global or regional climate variability?
are recent cold Northern Hemisphere winters due to a solar minimum? …. Maybe…
Is “global warming” due to increased solar activity?
No! – solar variability only drives max 0.2% insolation change - need 1% change - so we need greenhouse gas increase
what has caused short term cooling?
Volcanic eruptions have caused major short term cooling
how do volcanoes cause cooling?
Plumes from the largest eruptions may ascend at speeds from 10 m/s to > 200m/s and rapidly reach stratospheric heights exceeding 30 km
Subsequently get slow process of gravitational settling
what happened in 1991?
Eruption of Mt Pinatubo in the Philippines in June 1991 input larger ash volume to the atmosphere than Krakatoa.
where do troicpal thunderstorms top out?
stratosphere
what happened within 5 months of Pinatubo volcano?
stratospheric aerosol optical depth from + 40° N to 40° S increases by 2 orders of magnitude.
what does underlying warming cause?
Simulations with natural & anthropogenic forcing - only short cooler episodes
what does without underlying warming cause?
Simulations with natural forcing only show net cooling effect of eruptions
can volcanic and impact events radically change the climate?
yes, yet they are unpredictab;e. however, no known asteroids are heading at us now.
what is the hockey stick?
shows the global temperature change in the last 1000 years.
has global warming stopped over past 1999-2014?
no-oceans are still warming, sea levels are still rising, ice is still melting.
what years are the top 5 warmest?
- 2017, 2018 and 2014
how do we date past ice ages?
Use evidence based on isotopic fractionation The lighter oxygen isotope 16O becomes enriched in snow
The oceans become richer in the heavier isotope 18O
Followed 41,000 year cycle then changed to 100,000 year cycle.
what did Milankovitch suggest about the earths orbital?
Milutin Milankovitch (1920) suggested that variations in the Earth’s orbital parameters altered incident solar radiation and its distribution sufficiently to control the timing of the ice ages
what did Milankovitch think about isotopes?
Milankovitch’s ideas originally dismissed by physicists because changes in insolation were slight – it then took until 1976 for O isotope records from deep sea cores to prove that these orbital periodicities drove the ice ages. “ The climate is chaotic and only very slight changes are required to “tip” the Earth system from one mode into another.
how can the orbital variations be calculated?
The magnitude of changes in insolation due to the orbital variations can be calculated back (and forward) in time by astronomers.
what are interglacial cycles?
We can put this together with our marine O isotope and seal level records to look at CO2 variation through the most recent glacial – interglacial cycles
what did the interglacial cycles show?
Past natural variability during glacial – interglacial cycles was around 80 ppmv total (from 200 – 280 ppmv)
We passed 400 ppmv in 2013
in short term, the main carbon reservoirs which need t be taken into accont in the greenhouse warming debate are?
- the atmosphere (CO2 gas)
- the ocean (total dissolved inorganic carbon)
- the biosphere (organic carbon)
- the geological reservoir is also important: (fossil fuels !)
what is the carbon reservour the atmosphere?
Past natural variability during glacial – interglacial cycles was around 80 ppmv total (from 200 – 280 ppmv)
Increasing and we passed 400 ppmv in May 2013 ! Now – 2019 - at > 410 ppmv
CO2 annual emissions from fossil fuel use and cement manufacture, based on data of British Petroleum
cement is amso causing it to go up, as CaO andclay produce cement. CO2 rpoduced by combusion and calcination.
what is the carbon reservoir- the ocean?
The “organic” carbon cycle:
H2O + CO2 <==> CH2O + O2 photosynthesis - dominant in surface waters and respiration - dominant in intermediate and deep waters
This is the “ biological pump ” of carbon into the deep sea target for “geo-engineering” – increase primary production
– increase CO2 draw down from atmosphere The inorganic carbon cycle: Ca2+ + 2HCO3- <==> CaCO3 + CO2 + H2O carbonate formation - dominant in surface waters and dissolution - dominant at depth
Quick recap on Oceanic Carbon Cycle Equilibration with an atmosphere with enhanced CO2 will cause higher pCO2 throughout the ocean
Result: the ocean, in particular the deep sea, becomes more acidic and more corrosive to carbonates:
CaCO3 + CO2 + H2O ==> Ca2+ + 2HCO3
ocean continues to acidify
how can we stop CO2 rises and by when?
CO2 emissions must start to decline before 2100 to reach these targets.
Unless we drastically cut emissions now – we are heading for an overall 300% increase over natural levels.
what does RCP stand for?
Representative Concentration Pathways
what is the paris agreement?
2015 - 2°C
“to keep global temperature rise this century well below 2°C above pre-industrial levels… and to pursue efforts to limit the T increase even further to 1.5°C”
why is the limit of 2 degrees not enough?
“Right now we are facing a man-made disaster of global scale, our greatest threat in thousands of years: climate change.
If we don’t take action, the collapse of our civilisations and the extinction of much of the natural world is on the horizon
