Evidence of Climate Change (Temperature)
Climate Change: Physical Evidence & Global Impacts
Visible changes worldwide:
Sea level rise, melting ice sheets, and cryosphere decline
Extreme precipitation—> flooding in some regions
Severe droughts —> crop failure in others
Regional impacts:
Arctic & Antarctic warming rapidly
Deserts expanding into once-arable land
Temperate zones: milder winters, earlier springs, more heatwaves
Island nations and deltas: facing sea level threats
Future Outlook:
Rising global temperatures projected to continue
Climate change is real, dangerous, and already impacting millions
Climate zones
(a) The world’s major biomes with their physical environment
Climate change from global warming threatens to disrupt them, especially those already stressed by human activity
(b) Ecological sensitivity in the 21st century:
Map shows the projected percentage of ecosystems likely to undergo changes in plant species by 2100 due to human-induced climate change
Global Temperature
Global temperature reflects long-term average changes, not local weather
Data accounts for seasonal & regional variability
Expressed as temperature anomalies (differences from baseline), not actual degrees C
Earth’s energy balance:
For millions of years, Earth maintained energy equilibrium
Even small imbalances can cause significant climate shifts
Regional climate changes (e.g., Sahara, Amazon, Siberia) may not align with global trends due to natural variability
To detect true global warming:
Measure incoming vs outgoing radiation at the top of the atmosphere
Positive energy imbalance= evidence of global warming
Satellite data show a small but significant imbalance (<1.5 W/m²)— difficult to detect, but scientifically meaningful
Estimating Global Temperature
How Scientists calculate Global Temperature
Earth is divided into a 2 degree by 2 degree grid (or higher resolution)
Average temperature is calculated in each grid bo by using available data
Global temperature = weighted average of all grid boxes, correcting for Earth’s curvature (smaller boxes nears poles)
Challenges:
Sparse data in remote areas (poles, deserts, forests)
Ocean air temperature is mainly measured along coasts, shipping lanes, and buoys
Despite gaps, this method allows comparison with historic records to track global trends
Satellites vs surface thermometers
Satellites measure Earth’s energy imbalance at the top of the atmosphere (inflow vs outflow of energy)
This tells us about the overall climate system’s heating or cooling trend, but not how the energy is distributed
Surface thermometers directly measure the air temperature where people are, ecosystems, and infrastructure exist
They provide long, continuous records (going back ~150 years), which are essential for tracking climate change at regional and local scales
In short: satellites show the “energy budget” of the planet, while thermometers show the actual temperature changes we experience on the ground
Global climate network temperature stations
Global temperature estimates also use marine sea surface temperature data
Coverage gaps remain in remote land areas and oceans
Why Use Temperature Anomalies?
Temperature anomalies show how much temperatures deviate from a long-term average at the same location.
The base period (usually a minimum of 30 years) is critical for accuracy
This helps smooth out short-term effects like El Niño or volcanic eruptions
A poorly chosen base period can distort trends by exaggerating or understanding warming
Common base periods used:
Different climate organizations use different 30-year periods, tailored to their datasets and research goals
1951-1980 Goddard Institute for Space Studies
1961-1990 Climate Research Unit
1971-2000 NOAA
1979-1998 Remote Sensing Systems
1991-2020 University of Alabama at Huntsville
The entire 20th century National Climate Data Center
1850-1900 IPCC Sixth Assessment Report
Why Use Temperature Anomalies Instead of Absolute Temperatures?
Different organizations use different baseline periods, affecting the size of anomalies but not the trend or the overall magnitude of warming
For example, the University of Alabama in Huntsville (UAH) uses a baseline excluding earlier warm decades, making anomalies appear smaller
Anomalies are preferred because:
They are spatially consistent— similar up to 1,200 km from a data point, allowing estimates in remote areas
They reduce station bias— avoiding issues like altitude, urban heat, or placement
The Temperature Data
Temperature data are often misunderstood, yet they are essential to climate science. By combining land and ocean data, scientists can accurately track how much extra energy is accumulating in Earth’s system
Land Surface Temperature
Long-term Temperature monitoring
Thousands of weather stations worldwide
Use simple thermometers to record land surface temperature
Some stations have records spanning centuries
Key organizations collecting & publishing Data
NOAA- National Centers for Environmental Information (USA)
NASA GISS — Goddard Institute for Space Studies
JMA— Japanese Meteorological Agency
Berkeley Earth— Independent climate data initiative
HadCRUT— Collaboration between the UK Met Office’s Hadley Centre & University of East Anglia’s Climate Research Unit
Ocean Air and Sea Surface Temperature
Measuring Ocean Air Temperature
Collected on commercial/naval vessels
Limited coverage: confined to shipping lanes
Daytime readings affected by thermometer location
Nighttime data is more reliable but incomplete
Sea Surface Temperature (SST) is the temperature of the ocean’s uppermost layer, usually the top few centimeters to a few meters, depending on how it’s measured
It’s a key climate variable because it influences weather patterns, ocean currents, and energy exchange between the ocean and atmosphere
SST tells how warm or cold the ocean surface is
Thus, SST is preferred because
SST closely correlates with air temperature above
Provides more consistent and comprehensive data
Reduces biases from thermometer placement
Combined land-ocean data provides near-global coverage and critical insight into climate trends
Air Balloons
Upper-Air Observations with balloons
Over 900 global observation stations, mostly in the northern Hemisphere
Use weather balloons equipped with radiosondes
Radiosondes Measure
Air Temperature
Humidity
Atmospheric Pressure
Their purpose is to
Track temperature changes with height
Monitor how the middle and upper atmosphere responds to global warming
Critical data to understand GHG effects on atmospheric layers
Satellites
Satellites measure air temperature at different levels in the atmosphere
By using microwave sounding units (MSUs) instruments that measure the temperature-dependent microwave flux generated by oxygen molecules in the atmosphere
Since 1978: NASA & NOAA Satellites
Extend and enhance land and ocean records
Key data sets from:
University of Alabama at Huntsville (UAH)
Remote Sensing Systems (RSS)
Data corrections Required:
Orbital drift
Sensor variation
Time of day
Satellites and SST
Since 1967: Monitoring Oceans from Space
Satellites detect thermal infrared radiation emitted by the ocean
Radiation intensity and wavelength are temperature-dependent
Enables calculation of SST
Modern Technology
Satellites use Advanced Very-High-Resolution Radiometer (AVHRR) to provide global coverage of SST, but land surface temperature is more difficult to determine due to the impact of topography on the reflected signal
Land vs Ocean
SST is easier to measure via satellite
Land surface temperature (LST) is harder to assess accurately due to:
Topography
Reflected signal interference
LST is measured using thermal infrared sensors (satellites or ground instruments, e.g., MODIS, Landsat, Sentinel-3) supported by ground-based validation to correct for topography and signal interference
Global Historic Climatology Network
Global Historic Climatology Network (GHCN)
Maintained by NOAA’s National Climate Data Center (NCDC)
Largest international temperature data set
Data from 100,000+ stations in 180 countries
GHCN-M version 4 includes 26,000+ stations with a minimum of 10 years of data
Oldest continuous record: Berlin, since 1701
Data Quality
Older thermometers= less accurate, but highly precise
Allows reliable use of temperature anomalies (relative change)
Merged Global Temperature Record
Combines:
GHCN-M v4 (land)
Extended reconstructed Sea Surface Temperature (ERSST) (ocean)
Produces global temperature anomalies from 1880 to present
Missing Data
Challenge: Sparse Data at the Poles
Large parts of Arctic & Antarctic lack complete temperature records
Arctic warming faster than global average, must be included in global analysis
Two Approaches to fill missing data
1. GISS Model (NASA Goddard Institute for Space Studies)
Extrapolates temperatures up to 1,200 km from known stations
Captures regional trends, but may introduce errors doe to Arctic complexity
2. CRU/HadCRUT Model (UK Met Office & University of East Anglia)
Older CRU models assumed temperatures follow Northern hemisphere trends
Likely underestimated warming
HadCRUT5 (updated):
Offers both non-infilled and infilled versions
Infilled model extends anomalies beyond direct measurements
More closely aligned with GISS
GISS & HadCRUT5 infilled models reflect more accurate global warming trends
CRU is more conservative, but all models are grounded in robust science
Accuracy & Precision
Accuracy: How close a measurement is the the true or accepted value
Precision: How close repeated measurements are to each other, regardless of whether they’re correct
Accuracy is correctness, precision is consistency