Observed Climate Change

Flashcards covering key vocabulary and concepts related to observed climate change, including temperature measurements, data collection methods, and evidence of climate change effects on Earth's systems.

Proxy Records

• Used to calculate or estimate temperature changes over the last 65 million years

• indicates changes in rainfall and other weather but does not measure it directly.

Temperatures

• temp cycles linked to glacial and interglacial periods

• small changes in Earth’s orbits around the sun set in motion large changes in Earth System

• processes operating over 10k - 100k years timescales

Mount Loa CO2 Charting - changes in CO2 concentration

Charts carbon dioxide levels in the atmosphere over a long period, showing a steady rise since measurements began in 1958.

Human-induced CO2 Rate Today

Approximately 203 ppm/year, contributing to an increase in atmospheric opacity and radiation imbalance.

CO2 has been higher in the pst e.g. 65 million years to 2 million years ago

Importance of C02

• CO2 important for radiation balance

• as Co2 increases atmosphere is more opaque - infrared radiation = radiation imbalance

Changes in global temperature - how to calculate it

Satellite Data Sets

Available since the late 1970s to 1980s, used to track changes in global temperature using anomalies relative to mean temperature.

Anomalies

Temperature measurements that are relative to mean temperature, used to avoid biases in global data sets.

measuring temperatures - sea surface temperatures

• relying on buckets in the 20th century

• biases associated with the bucket method

• water evaporating in bucket as lifting it so it would seem colder than it is

• last 40 years now have buoys

recent records of temperature

Land and Ocean temperatures

• Land tends to warm faster than oceans

• Evaporation over oceans offsets warming relative to land which tends to be drier

Atmospheric temperature trends

• Measured by:

• Radiosondes - Instruments attached to weather balloons, used to record atmospheric conditions up to the top of the atmosphere

• Satellites

• Reanalysis (models which incorporate various observational data)

Lower-tropospheric temperature are increasing

• Vertical distribution of temperature change in troposphere is important for atmospheric stability

Stratosphere is cooling

• key evidence of climate change

• warming troposphere and cooling stratosphere

• reason for cooling - 80s/90s - depletion of ozone - less radiation being absorbed by ozone

• increase in greenhouse gases in troposphere - less energy in infrared part - less energy in stratosphere

Ocean Heat Content

Tracks changes in the oceans, which store approximately 90% of excess heat energy in the Earth's climate system due to GHG-induced radiative imbalance.

Atmosphere has low specific heat capacity compared to oceans

Heat stored by oceans will be released to surface

Argo Floats - Ocean heat content measurement

Launched from ships to drift around the surface, descend to 1000m and then 2000m, measuring temperature changes and sending data back to satellites.

Ocean heat content anomalies + uncertainties by depth

Reference Glaciers

Representative glaciers in different regions that have all decreased in mass over the past 70 years due to more ablation than input.

Ice sheets over continental regions - both Greenland and Artic

Artic slightly lower

Sea level rise - Tidal Gages

Located at coastlines and estuaries, used to measure sea level rise relative to land; now supplemented by satellite data.

Global sea level trends - Active Remote Sensing

Technique involving sending a pulse down and measuring the time taken for it to return, used to determine depth.

most of the earth has experienced sea level rises

Sea level change

• rates of local sea level on coast can be:

• larger than global average due to geological processes like ground setting

• smaller than global average due to processes like the centuries-long rebound of land masses from the loss of ice-age glaciers

Reasons for sea level rise

• thermal expansion

• added water, mostly due to glacier melt

• between 1993 + 2018:

• melting ice sheets and glaciers accounted for 44% of sea level rise

• thermal expansion of water accounted for another 42% thermal expansion of water

Summary