week 4 Flashcards
(26 cards)
What was the living atmosphere like from 3.3BYA to 500 MYA?
around 3.3 BYA:
-condensation of water vapour which formed the oceans we have today
-development of oxygen in the atmosphere= first life forms that evolved on the planet were photosynthetic cyanobacteria
-Increasing levels of oxygen were accompanied by an increase in ozone through the photo-dissociation of water via the Chapman mechanism
around 1.6BYA:
-oxygen content of the atmosphere was approximately 1% of current oxygen levels
Cyanobacteria were also important in the origin and development of plant life, as chloroplasts within plant cells are actually cyanobacteria that took up residence within certain eukaryote cells sometime in the late Proterozoic or early Cambrian eras, helping develop plant life on land
What is the modern atmosphere like- 500MYA to present?
-nitrogen (N2) at 78%
-oxygen (O2) at 21%
-argon (Ar) at 0.93%.
-carbon dioxide (CO2) only 0.03%
-methane (CH4) is even lower at 0.0018%.
-water vapour (H2O), ranging from about 0.2% to 2.6%.
How has forest clearance changed over the years? make reference to figure
The sources reference a map showing forest cover in Europe in 1000 BC and AD 1500. In 1000 BC, most of Europe, as shown, was essentially covered in forest, about 90%. By AD 1500, approximately 2,500 years later, forest cover had been reduced to 17%
What did John Tyndall do?
Professor John Tyndall was instrumental in developing what is now called the greenhouse effect
-stated that “the atmosphere admits of the entrance of the solar heat, but checks its exit; and the result is a tendency to accumulate heat at the surface of the planet”
-used the first ratio spectrophotometer instrument to measure how different gases interacted with radiation
-found that basic gases like hydrogen, nitrogen, and oxygen had hardly any measurable absorption, but water vapour and carbon dioxide showed extremely high absorption capabilities
What evidence exists to show the emissions and temperature relationship?
- greenhouse gas concentrations
- radiative forcing
- temperature trends
- rate of temperature trend
- rate of temperature trend
- ocean warming
- extreme events
What green house gas evidence exists to show the emissions and temperature relationship?
-significant global increase in carbon dioxide concentrations since the pre-industrial era (before 1800).
-CO2 concentrations increased by about 35% from pre-industrial levels to the early 2000s. –methane concentrations also increased significantly, by 142% over the same period, although its concentration is much lower than CO2.
-nitrous oxide has also increased. These increases are unprecedented in at least the last 800,000 years
What radiative forcing evidence exists to show the emissions and temperature relationship?
increase in these greenhouse gases leads to a positive radiative forcing, meaning they cause more absorption of outgoing long-wave radiation from the Earth, resulting in a heating effect
What temperature trends exist as evidence to show the emissions and temperature relationship?
temp trends show an upward rise especially since the mid-20th century, is considered very likely due to the increase in anthropogenic greenhouse gas concentrations
What rate of temperature change observations exist as evidence to show the emissions and temperature relationship?
rate was about 0.045°C per decade over the past 150 years, it was about 0.074°C over the past 100 years, 0.128°C over the past 50 years, and approximately 0.177°C per decade over the last 25 years
0.19 ± 0.02 °C per decade from 1970-2023, compared to 0.04 ± 0.01 °C per decade from 1880-1969
so clear acceleration
How do ocean warming observations exist as evidence to show the emissions and temperature relationship?
the ocean heat content (OHC) shows a trend very similar to atmospheric temperature, indicating the ocean is warming up
How do extreme event observations exist as evidence to show the emissions and temperature relationship?
Changes in the frequency and intensity of daily temperature extremes since the mid-20th century are very likely linked to human influence, and human influence is likely to have more than doubled the probability of heat waves in some locations
What are the data sources for greenhouse gas concentrations?
Two main sources:
Ice Cores:
-before 1958 main source- still used now
-Little bubbles of air trapped within the ice preserve samples of the atmosphere from the time the ice formed
-Gases can be extracted from these bubbles to measure past atmospheric concentrations
-age of the ice is known as a function of depth
Direct Atmospheric Measurements:
-After 1957-1958
-measurements of carbon dioxide in the atmosphere began, providing higher resolution and continuous data
-first such measurement station was set up by Charles David Keeling on Mauna Loa, Hawaii
-also got some in South Pole, Pacific coast etc
Satellites also provide measurements of greenhouse gas concentrations, which can be used to validate surface measurements
What is the Keeling curve?
Keeling Curve is a graph showing the continuous measurement of ambient carbon dioxide concentrations in the atmosphere, initiated by Charles David Keeling at Mauna Loa, Hawaii
-provided the first significant evidence of rapidly increasing carbon dioxide due to man-made emissions
-longest-running direct measurement of CO2 in the atmosphere
-curve shows a clear upward trend in CO2 concentration over time
-famous “sawtooth” pattern, which reflects the natural seasonal variation caused by photosynthesis by plants in the Northern Hemisphere
What is the historical trend? Refer to sources and figures
The increase from pre-industrial levels (around 280 ppm) to around 390 ppm in 2010 represented a 39% increase, but by early 2025, reaching over 420 ppm represents a 50% increase compared to the original analysis
research has mainly used ice cores
What are the sources of data for temperatures?
Tree Rings:
-provide information going back almost 10,000 years
-width of tree rings reflects growth= influenced by factors like water vapour and temperature
Ice Cores:
-date back approximately 800,000 years
-temp estimates from the isotopic ratios of oxygen measured in the ice.
-ratio of heavier oxygen isotopes indicates the temperature at which water condensation occurred
Ocean Sediments:
-data extending back millions of years. -proportion of heavy oxygen isotopes in sea cells within sediments indicates past temperatures (the proportion goes up when temperatures go down).
-identify hot and cold episodes or glacial periods over geological timescales
Surface Observations:
-thousands of daily temperature observations
-land temps come from about 1,300 observing stations producing monthly averages for climate research
Sea Surface Temperature Observations:
-buoys deployed in the ocean (fixed and floating) and meteorological instruments placed on ships in the Voluntary Observing Ship Programme= approx 1.5 million observations each month.
Satellites:
-global temperature data of the lower atmosphere since around 1979
-their trends follow surface temperature trends quite nicely
What is the correlation between CO2 and concentration and temperature change?
very strong correlation between atmospheric CO2 concentration and temperature change over the last 160,000 years
this increase in CO2, in turn, caused the entire planet to warm further via the increased greenhouse effect. Overall, about 90% of the global warming occurred after the CO2 started to increase. Therefore, CO2 acted as a positive feedback that significantly amplified the initial orbitally-forced warming.
Where does air-ocean temperature data come from?
Land temperature:
1,300 observing stations monthly. These stations take daily readings and create monthly averages for climate researchers
Sea Surface Temperature (SST):
buoys (fixed and floating) deployed in oceans worldwide and from ships participating in the Voluntary Observing Ship Programme
Satellites: Since 1979, satellites have also provided global temperature data for the lower atmosphere
What are some examples of variations in the system?
- ENSO
- Volcanic eruptions
- Internal variability
The climate system also has internal variability, including phenomena like the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), which can account for some temperature fluctuations over decadal timescales - Solar Variation
(others discussed further in week 3)
What are the key points used as evidence from WMO 2024 and 2025?
-the past ten years (2015-2024) are now the ten warmest years on record
-We have likely seen the first calendar year with a global mean temperature of more than 1.5°C above the 1850-1900 pre-industrial average
-evidence is based on six international datasets that reach this conclusion
-2024 saw exceptional land and sea surface temperatures and ocean heat increases, indicating the entire atmosphere and ocean system is responding to CO2 emissions
-Regarding the Paris Agreement goal of 1.5°C, the WMO stated it is not yet “dead” but is in very great danger
What are some of the controversies?
Argument 1: “The Earth’s climate is always changing and this is nothing to do with humans”. This argument suggests that current climate changes are merely part of natural Earth cycles.
Argument 2: “Rises in the levels of carbon dioxide in the atmosphere are the result of increased temperatures, not the other way round”. This argument is based on observations from long-term historical data (like ice cores) where a rise in carbon dioxide appeared to lag behind a rise in temperatures by hundreds to thousands of years. Proponents argued that if CO2 followed temperature, it could not have caused the temperature rise
What is the response to these arguments?
Response to Argument 1: The current rate and magnitude of change, particularly in CO2 concentrations and temperature, are unprecedented compared to past natural variations seen in the long-term ice core record stretching back 800,000 years
Response to Argument 2: Argument that CO2 lags temperature in historical records is true but is an incomplete and misleading argument.
the CO2 increase acted as a powerful positive feedback that caused about 90% of the total warming
What are some of the weather extremes observed (focus on storms like Hurricaine Katrina)?
Hurricane Katrina in 2005 is given as an example of a significant extreme weather event
-Category 5 storm with maximum sustained winds above 170 miles per hour
Monitoring of tropical storms and hurricanes since the early 2000s shows an apparent rise in their occurrence
-very likely that human influence has contributed to observed global scale changes in the frequency and intensity of daily temperature extremes since the mid-20th century
How vulnerable are we to sea level rise?
total increase in sea level has been about 20 centimetres since 1900
Parts of the UK are highlighted as potentially vulnerable, particularly coastal areas and large estuaries. Bangladesh is considered particularly vulnerable, as is Florida
Potential future storms can exacerbate the risk by inundating coastal regions.
While there are estimates for future sea level rise, there are large uncertainties, with estimates ranging from 20 cm to 2 m
How has ice mass changed/going to change? Name figures etc as evidence.
-The largest contributions to global glacier ice loss over the last decade have come from glaciers in Alaska, the Canadian Arctic, the periphery of the Greenland ice sheet, the Southern Andes, and the Asian mountains, collectively accounting for over 80% of the total ice loss
current glacier extents are out of balance with current climatic conditions, indicating that glaciers will continue to shrink in the future even without further temperature increase
The Arctic sea ice extent (in millions of square kilometers) has been decreasing, although blips of changes occur
