Climate Science Flashcards
what is a time series?
A time series is a sequence of data points or observations collected or recorded at specific time intervals, typically at equally spaced time points.
what is an anomaly?
An anomaly is a departure of a climate variable (e.g., temperature) from a reference value, usually a long-term average over a defined reference period
name 2 common ways in which se surface temperature (SST) has been measured
and which method led to warmer readings?
- engine intake water
- buckets
engine intake water was a tenth of degree warmer on average
why is the northern hemisphere warmer?
because it has more land, which has a much lower specific heat capacity than water
The World Meteorological Organization (WMO) defines climate as:
the 30-year average weather
BUT: the length of averaging to be confident in a long-term change depends on the variability
on a timeseries, what is a hiatus and a surge?
- Hiatus refers to a period within a time series where there is a temporary interruption or pause in the expected or typical trend or pattern.
- A surge in a time series refers to a sudden and significant increase or spike in the data values over a relatively short period.
why is the troposphere warming and the stratosphere cooling?
Troposphere gets warmer because it absorbs the heat from the earth (with the CO2 it contains), this means less heat will reach the stratosphere
Much like when you put a blanket on, you will get warmer but your room will cool down because you are no longer heating it
How do we understand the climate before we had instrumental measurements? provide examples
- Climate proxies
- A climate proxy is a measurable physical or biological indicator that provides information about past climate conditions.
- e.g. tree rings, ice cores, coral, pollen, fossils, sediment cores
what was the medieval warm period?
The Medieval Warm Period, also known as the Medieval Climate Anomaly, occurred roughly from around the 9th century to the 14th century (approximately 950 to 1250 AD).
During this period, parts of the Northern Hemisphere experienced relatively warmer temperatures compared to the preceding and succeeding centuries.
what was the ‘little ice age’?
The Little Ice Age was a cooler climatic period that occurred from roughly the 14th century to the 19th century (approximately 1300 to 1850 AD).
The LIA was characterized by colder temperatures, especially in the Northern Hemisphere, with periods of more frequent and severe cold spells, harsh winters, and glacial advances.
what are the 2 kinds of ‘natural variability’?
- “Internal” variability
Behaviour of Earth’s chaotic system
No long-term trend - Naturally “forced”
Changes in the sun (now getting dimmer), Earth’s orbit (shifts), volcanoes
Can cause long-term trend
advantages and disadvantages of climate proxies
Advantages:
Very long record (potentially millions of years)
Disadvantages:
Often respond to several climate variables in a complex way
May have low resolution (space & time)
Must be preserved (record may be biased or ‘overprinted’)
what were the reconstruction methods for these periods?
- 1979 onwards
- 1850s - present
- 1kyear
- 5 kyear
- 200 kyear
- 800 kyear
- 2Myears
- 1979 onwards = satellite measurements of global temperatures
- 1850s - present = surface thermometers in widespread use
upper air measurements since 1950s - 1kyear = written records
- 5 kyear = tree rings – most trees considerably younger!
-Coral - 200 kyear = ice cores, lake sediments, cave deposits, ice-rafted debris
- 800 kyear = ocean sediment cores
- 2Myears = Quaternary sediments, pollen, etc.
what do tree rings tell us?
Broadly: wide ring = warm days and sufficient water; narrow ring = stressful conditions (e.g., water shortage)
In detail: a mixture of conditions is recorded
depends on what a given tree requires for growth, and what is limiting
More sensitive to summer than winter temperature
Many properties of a ring can be measured
width, density of early wood, density and width of wood grown late in the season
isotope chemistry of the wood composition of the rainfall, rate of photosynthesis, etc.
in the 1960s what happens to tree ring data?
For reasons that are not yet understood, temperatures derived from tree rings started to diverge from measured temperatures
what is the CET? and when did it begin?
Central England Temperature (CET) from 1659 CE until present, so the longest climate record available in the world
what were some characteristics of the medieval climate anomaly?
- Limits of cultivation were higher on hills than in later centuries
- Vineyards in the UK
The upper tree line was higher than earlier or later times - Several periods of prolonged drought
-very narrow tree rings
-evidence suggesting a predominance of “anticyclonic” weather over Northern Europe
is sea level a reliable climate indicator?
Yes, it has a good correlation with reconstructed temperatures and is well recorded geologically
was the latest decade warmer than any multi-century period after the last interglacial, around 125,000 years ago?
yes
climate myth!:
Scientists in the 1970s predicted an ice age
This isn’t exactly a myth – it was a published result from prominent climate scientists, but the research was taken far out of context in media articles, and the consensus amongst scientists was that greenhouse warming was the bigger problem
(because of aerosols, which were delt with in the 80s, potentially preventing this ice age)
how does the mid-pliocene’s (3-3.3 million years ago) climate compare with today’s?
it had similar levels of CO2 (360-400ppm) but was much warmer (3.2 degrees warmer) and had a higher sea level (5-25m), scientists unsure why
how does the cenozoic era’s (last 66M years) climate compare with todays’s?
CO2 up to >5 times present day (7 times pre-industrial)
Reduced through silicate weathering etc.
Global temp. up to 8-10 °C higher than today during ‘Greenhouse’ times
Overall descent into ‘icehouse’
how do the stats of the mid-pliocene (3.3-3M years ago) compare to today’s?
- Atmospheric CO2 estimated to be 360-400 ppm (now 402-420ppm)
- Continental configurations were similar to present
- Many plant and animal species also exist today
- Orbital configuration similar to present (global mean insolation = –0.022 W m–2 relative to present)
- Global mean air temperature 3.2 °C warmer
- Sea level 5-25 m higher
High latitude ocean SSTs were 7 °C higher than 1850-1900 - Tree line 2000 km further north in Canadian Arctic
- High latitude air temperatures 10-20 °C higher
when did the current ice age begin?
The current ice age, known as the Quaternary glaciation, began approximately 2.58 million years ago during the Pleistocene epoch
Reconstructing temperature using ice cores (why it works)
- Known fraction of H218O to H216O in evaporated water (about 0.19%)
- Greater fraction of H218O condenses than H216O
- Lots of H218O in precipitation
- Air moves north and gets colder
- Strong depletion of H218O in precipitation relative to H216O
what is a power spectrum?
A power spectrum is a mathematical tool used in signal processing, physics, astronomy, and other fields to analyze the frequency content of a signal or time series. It represents the distribution of power (or energy) across different frequencies within the signal.
what did serbian mathematician Milutin Milankovic propose in 1920?
that variations in Earth’s orbit would influence climate
watch this video on orbital variations and make some flashcards on it
https://www.youtube.com/watch?v=ZD8THEz18gc
Earth’s axis of rotation is tilted relative to the orbital plane
Currently the tilt (obliquity) is …..
Tilt varies between about ….. and ….. with a period of around ……
- 23.5°
- 22.1°
- 24.5°
- 41 ka
large obliquity leads to….
more exaggerated seasons
When the axis points toward the Sun in perihelion (i.e. the north pole is pointed towards the Sun)……
the northern hemisphere has a greater difference between the seasons while the southern hemisphere has milder seasons.
The period of precession of the Earth’s orbit is complicated by other planets (mainly Jupiter); (how long is the period)
it is between 19 and 21 ka (but really 26Ka)
The orbit affects the latitudinal distribution of solar radiation
jj
what are Dansgaard-Oeschger oscillations
Dansgaard-Oeschger (D-O) oscillations are rapid climate fluctuations that occurred during the last glacial period, approximately every 1,500 years. These events are characterized by abrupt warming (5-8°C) followed by **gradual cooling **and have been primarily identified in Greenland ice core records.
(they don’t occur during interglacials)
Abrupt climate changes during deglaciation:
- Solar insolation of the NH increased
- Ice sheets receded
- CO2 rose to present-day levels
- Temperature rose sharply 5oC
what was the Bølling-Warming event?
- it happened about 15k years ago
- 4-5 °C N. Hemisphere warming in few decades
- Change in meltwater routing → disrupted North Atlantic ocean circulation
→ reduced poleward heat transport
climate myth:! Global temperatures were higher in the early Holocene (8000-10000 years ago) and it was even called the “climate optimum”, which again shows that there’s nothing unusual about today’s climate change
Indeed, it almost certainly was warm in that period, but today’s global mean temperatures now exceed those in the early Holocene. Nevertheless, climate reconstructions remain uncertain, so there still a lot to be learned about natural climate variability
Climate of the Holocene (last 12 kyr):
- Relatively stable climate in the Holocene
- Early Holocene warmer than late Holocene, but still an open question
- Cooling trend is not understood
– Climate models don’t reproduce it
what is meant by ‘energy balance’?
Energy balance means that the energy absorbed by an object is equal to the energy it gives out (emits)
Energy balance determines the temperature of an object
e.g. Energy absorbed from the sun must equal energy emitted by Earth to space
what does incoming solar radiation consist of?
Shortwave:
- UV
- visible light
- near-infared
what does outgoing terrestrial radiation consist of?
- longwave/ infared radiation
-this is what is absorbed by greenhouse gases
Earth receives energy from the sun (solar radiation) at a rate of…
Averaged over all latitudes, this is…
…1368 W/m2 (Watts per square metre)
averaged over all latitudes this is 1/4×1368 W/m2 = 342 W/m2
Earth’s atmosphere has a heat capacity of…
700 J/kg/K
Earth’s atmosphere weighs about…
3.5x10^18 kg
Earth has a surface area of…
5x10^14 m^2
what is the formula for ‘energy emitted’
E = sT^4
where - E = radiative energy flux (W/m2)
- T = absolute temperature (K = oC+273.15)
- s (sigma) = Stefan-Boltzmann constant (5.67x10-8 W/m2/K4)
A fraction of incoming solar radiation is reflected back to space and plays no role in the energy balance of the planet. This fraction is called the
planetary albedo
Earth’s global average albedo = 0.3
therefore 30% of incoming solar radiation is reflected
Ratio of actually emitted radiation to maximum possible is the…
emissivity, e (epsilon)
The solar flux at 50 °N is ……… of its value at the equator
cosine(50°)
what is earths emissivity measured from space?
~0.61
