Climate change prior to 1900

The ice core record indicates that greenhouse gases co-varied with antarctic temperature over glacial-interglacial cycles, suggesting a close link between natural atmospheric greenhouse gas variations and temperature. Variations in CO2 over the last 420 kyr broadly followed antarctic temperature, typically by several centuries to a millennium (Mudelsee, 2001).

The sequence of climatic forcings and responses during deglaciations (transitions from full glacial conditions to warm interglacials) are well documented. High-resolution ice core records of temperature proxies and CO2 during deglaciation indicates that antarctic temperature starts to rise several hundred years before CO2 (Monnin et al., 2001; Caillon et al., 2003). During the last deglaciation, and likely also the three previous ones, the onset of warming at both high southern and northern latitudes preceded by several thousand years the first signals of significant sea level increase resulting from the melting of the northern ice sheets linked with the rapid warming at high northern latitudes (Petit et al., 1999; Shackleton, 2000; Pépin et al., 2001). IPCC, 4th Report, 2007

(A) The ice-equivalent eustatic sea level history over the last glacial-interglacial cycle according to the analysis of Waelbroeck et al. (2002). The smooth black line defines the mid-point of their estimates for each age and the surrounding hatched region provides an estimate of error. The red line is the prediction of the ICE-5G(VM2) (B) The fit of the ICE-5G(VM2) model prediction (red line) to the extended coral-based record of RSL history from the island of Barbados in the Caribbean Sea (Fairbanks, 1989; Peltier and Fairbanks, 2006) over the age range from 32 ka to present. The actual ice- equivalent eustatic sea level curve for this model is shown as the step- discontinuous brown line. The individual coral-based estimates of RSL (blue) have an attached error bar that depends upon the coral species. The data denoted by the coloured crosses are from the ice- equivalent eustatic sea level reconstruction of Lambeck and Chappell (2001) for Barbados (cyan),Tahiti (grey), Huon (black), Bonaparte Gulf (orange) and Sunda Shelf (magenta). IPCC, 4th Report, 2007

Younger Dryas Towards the end of the last Ice Age, climate warmed, then suddenly cooled again for almost 1000 yrs Younger Dryas

The Younger Dryas saw a rapid return to glacial conditions in the higher latitudes of the Northern Hemisphere between 12,900 – 11,500 years before present (BP) in sharp contrast to the warming of the preceding interstadial deglaciation. The transitions each occurred over a period of a decade or so.Thermally fractionated nitrogen and argon isotope data from Greenland ice core GISP2 indicates that the summit of Greenland was ~15 °C colder than today during the Younger Dryas. In the UK, coleopteran (fossil beetle) evidence suggests mean annual temperature dropped to approximately -5 °C, and periglacial conditions prevailed in lowland areas, while icefields and glaciers formed in upland areas. Nothing of the size, extent, or rapidity of this period of abrupt climate change has been experienced since. The Younger Dryas

Possible Cause for the Younger Dryas North Atlantic deep water formation – cut off by the cap of relatively light freshwater Figure 15-2

Cameron Lee C., The Younger Dryas Period

The Atlantic Conveyor

Did the Younger Dryas was caused by the shutdown of the Atlantic Conveyor?

As the Laurentide ice sheet retreated, melt water was diverted from the Mississippi River to the St. Lawrence River North Atlantic ocean became capped with freshwater  not dense enough to sink  thermohaline circulation shut down for ~1000 yrs

Replacing salty oceans with fresh water could trigger a Positive Feedback Loop: No salty water than no downwelling No downwelling than less warm water reaching northern part of North Atlantic Less warm water than cooler air Cooler air than colder temperatures Colder than more intense sea ice growth More sea ice growth than glacier advance More ice than higher albedo Higher albedo than less heat in climate system and thus reinforces colder temperatures and sustains colder climate

TIME BP Northern EuropeNorth America Glaciers retreat in AlpsMajor collapse of part of ice sheets Wet period over US with lake levels showing highest levels around BP abrupt warming (~ BP) with forest expansion, known as Bölling interstadial Return to colder conditions, around BP for about 500 years, known as Older Dryas. Warming around BP, although colder than in Bölling, known as Allerød interstadial. Cordilleran ice sheet retreat Changes at the and of Last Ice Age Burroughs, Climate Change, 2001

TIME BP Northern EuropeNorth America Around BP a sudden and dramatic cooling, known as Younger Dryas Drainage of meltwater from Laurentide ice sheet switches from Gulf of Mexico to St Lawrence. Surges of iceberges out of Hudson Bay cooled the North Atlantic, probably triggering the Younger Dryas Around BP sharp and sustained warming, its initial stage is knows as Pre-Boreal Readvance of Laurentide ice sheet may redirected melting water back to Gulf of Mexico switching off the Younger Dryas Spreading of forests across northern Europe Cordilleran ice sheet melts rapidly and disappears at around BP Forests established at high latitudes, but fennoscandian ice sheet did not disappear until around 8500 BP. Laurentide ice sheet declines more slowly and finally melts at around 7000 BP. Burroughs, Climate Change, 2001

PeriodCentral EnglandEurope Boreal BC Temperatures: JA: 16.3; DJF: 3.2, annual: 9.3 ~1-2°C warmer than today Atlantic BC Temperatures: JA: 17.8; DJF: 5.2, annual: 10.7 Wetter than today Rapid peat build-up in N. Europe, but cold spells in Alps ( BC) Sub-boreal BC Temperatures: JA: 16.8; DJF: 3.7, annual: 9.7 Generally dry and warm until ~1500 BC, much cooler and wetter until ~1200 BC, than warmer Sub-atlantic 900 BC onwards Temperatures: JA: 15.1; DJF: 4.7, annual: 9.3 ( BC) (At present JA: 15.8; DJF: 4.2, annual: 9.4 ) Cooler, wetter BC, than warmer, drier until ~AD 400 than colder and more variable until ~AD 1000 Changes during the Holocene

PeriodSaharaNorth America Pre-boreal Lake Chad 52 m higher (area km 2 ) Boreal BC Wetter in EgyptLaurentide ice sheet expanded (Cochrane readvance BC) Atlantic BC Lake Chad still m higher than present, moist except BC Sharp cooling in White Mountains BC Sub-boreal BC Moist period ended ~2350 BC, thereafter much drier Cooling in White Mountains ~1200 BC. Northern Great Plains warmer (1- 2°C) and drier until ~2000 BC Sub-atlantic 900 BC onwards Generally arid but some evidence of more winter rain in North Africa Northern Great Plains drier than now until AD 1200; with extreme drought AD , , White Mountains coldest ~900 AD Changes during the Holocene

Climate change in the human history

Medieval Warm Period and Little Ice Age were the most evident climate fluctuations during last millenium

Medieval Warm Period - Medieval Climatic Optimum Although there is no evidence of sudden change there are some pointers to the fact that the climate of northern Europe became more warmer during the ninth and tenth centuries: Expansion of economic and agricultural activity to the north, Grain was grown in the Norway further north than today, Crops were grown in Britain at higher levels than it is economic today, Norse colonization of Iceland and Greenland. Tree rings evidence shown than warmer period in northern Fennoscandia lasted from 870 to 1100, but on Greenland warmer period lasted from around 600 to the fourteenth century.

Eric The Red was a Viking explorer. He was born in around 950 in Norway. His father was banished from Norway because he killed a man. In 982 Eric the Red was banished from Iceland for three years because he also killed a man. He sailed to Greenland. After three year he returned to Iceland and than led a group of colonists to Greenland in 986. His exploration to Greenland had 400 to 500 settlers in 14 ships

Farm under the Sand (Western Settlement) It happens in Greenland...that all that is taken there from other countries is costly there, because the country lies so far from other countries that people rarely travel there. Every item, with which they might help the country, they must buy from other countries, both iron and all the timber with which they build houses. People export these goods from there: goatskins, ox-hides, sealskins and the rope...which they cut out of the fish called walrus and which is called skin rope, and their tusks... The people have been christened, and have both churches and priests.... (King's Mirror, 13th c Norway)

The mild climatic period was fairy short lived, around ~ AD1200 the ever-increasing cold was making life extremely difficult, and after some years no supply ships were able to reach Greenland through the ice-choked seas. By about 1350, the settlements in southwestern Greenland had been abandoned. In 1408 a wedding was performed in the Hvalsey Church. It was not only the last service at Hvalsey, but also last written record of the Vicking presence in the region. Hvalsey Church, Greenland

The Little Ice Age ~1450 to 1900 A.D. Regional (global?) expansion of mountain glaciers Cooling of a few tenths of a degree C NW Europe, Western U.S., S. America Best explanation is – increased volcanism – decrease in sun’s radiation output Maunder Minimum

The little ice age ~1600 to ~1850 Extensive advance of glaciers in Europe Long, severe winters Was it global? Abraham Hondius, 1684 A Frost Fair on the Thames at Temple Stairs (1684)

Recent Warming since 1850 AD Coincident with Industrial Revolution and rapid and large increase in CO2

Climate changes in Europe Climate changes in south-eastern Asia Climate changes in Balitc Sea Region El-Nino Fourth Report of IPCC IPCC SREX Assessment of Climate Change for the Baltic Sea Basin wnloads/index.html