Geography Changing Climate

climate change definition

the long-term change in global/regional climate due largely to increased levels of CO2 in the atmosphere

the quaternary period + its epochs

a subdivision of geological time covering the last 2.6 mil years up to the present day.

1. pleistocene epoch: start of period - 11,700 years ago

2. holocene epoch: 11,700 years ago - now

ice ages

any period of time when the earth has permanent ice sheets

5 major ice ages in earth’s history. outside these the earth was ice free even at high latitudes. these were warm periods known as greenhouse periods

within ice ages are glacial periods (cold) and interglacial periods (warm)

we are in an ice age but in an interglacial period

climate proxies

reserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climactic conditions over a long fraction of the earth’s history

climate proxies: tree rings

trees add a new layer of material each year. wide thick rings indicate a fertile well-watered growing period, thin narrow rings indicate lower rainfall & less than idea growing conditions

climate proxies: ice cores

each year more snow/ice is added to the sheets of ice in the arctic & antarctic. scientists can drill down into ice and remove tubes of ice (ice cores)

ice cores can be used to study ice laid down 800k years ago

lighter sections are summer snow, darker sections are winter snow

they contain bubbles of gas that tell us what the air was like thousands of years ago. they contain different isotopes of oxygen and this can tell us whether the climate was warmer/colder

climate proxies: global temperature data

records of temps across the world began being kept from ~1880. today there are over 1,000 weather stations recording temps

scientists use records to study the earth’s temp and compare it to different time periods, work out global average temps, develop lists of hottest/coldest years

climate proxies: sea ice extent

arctic sea ice is shrinking quickly - photos from earliest 1900s can be compared with current ones e.g. satellite images / images from specific locations

comparing photos can show how much ice levels have reduced

but these aren’t very reliable as photos provide comparison not quantitative data. photos can be edited too

qualitative data

data about images, words, experiences (not numbers)

quantitative data

data about numbers (tends to be more useful as is more precise)

climate proxies: paintings & diaries

people made paintings/wrote diaries before cameras were invented or temps were recorded. so they can be used to gauge climate events further in the past

e.g. paintings & diary entries show that the river thames froze a bunch of times between 1300s - 1800s and this shows a colder time period (known as the ‘little ice age’)

natural causes of climate change: milankovitch cycles

in the 1930s milankovitch (a mathematician) argued that climate change was linked to the way the earth orbits the sun, how it wobbles, how it tilts. these three ideas are the milankovitch cycles

• obliquity - how the earth tilts on its axis

• precession - how the earth wobbles on its axis

• eccentricity - changes in the shape of the earth’s orbit

(obliquity = tilt, precession = wobbles, eccentricity = shape of orbit)

milankovitch cycles: eccentricity

the path of the earth as it orbits the sun, which isn’t fixed and changes over time from being almost circular to almost elliptical

one cycle (circular - elliptical - circular) takes 100,000 years

eccentricity may have caused the glacial & interglacial cycles of the quaternary period

orbit is more circular = colder periods (as sun is never close to earth)

orbit is more elliptical = warmer periods (as sun is sometimes really close to earth and when it’s far there isn’t enough time to freeze up again)

milankovitch cycles: precession

the earth wobbles as it spins on its axis (wierdo)

the wobble is caused by the force of gravity from the sun & moon

as the axis turns it slowly changes the direction it points in, tracing a circular shape (see picture)

it takes 23,000 years to go from one extreme to the other

this can change severity of seasons, which hemisphere is closer to the sun at different times, meaning some regions of the world have very long days & nights (eg northern norway)

milankovitch cycles: obliquity

the earth is tilted on its axis (wierdo)

over 400,000 years the angle changes from 21.5° to 24.5°. rn we are at an angle of 23.5°

less tilt = less extreme seasons (cool summers, warm winters)

more tilt = more extreme seasons (hot summers, cold winters)

natural causes of climate change: sunspots

the dark spots on the sun’s surface - temporary and caused by magnetic storms

more sunspots = more radiation earth recieves from the sun = higher temps

there is an 11 year cycle of sunspot activity (although some are longer)

the little ice age (1300-1870) is linked to a time when there were fewer sunspots, the medieval warm period is linked to more sunspots

natural causes of climate change: volcanoes

supervolcano = one that erupts more than 1000km³ of material at once

when volcanoes erupt they release lots of dust (containing ash, sulphur dioxide, water vapour) into the atmostphere, which blocks sunlight resulting in cooler temps

dust can be carried by winds across the globe, meaning cool temps everywhere

mount pinatubo in the philippines erupted on 15th june 1991 (charlie’s birthday) putting 20mil tones of sulphur dioxide & ash 20 miles into the atmosphere. this reduced global sunlight by 10% and cooled the planet by 1.3^o for 2yrs