Global Warming Primer

Global Warming Data and Evidence

References

• https://gml.noaa.gov/aggi/
• https://www.climate.gov/news-features/climate-qa/what-evidence-exists-earth-warming-and-humans-are-main-cause
• https://science.nasa.gov/climate-change/evidence/
• https://science.nasa.gov/earth/explore/earth-indicators/global-temperature/
• https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature
• https://www.climate.gov/climatedashboard

Global Warming Recap

So, we’ve learned that the Earth’s greenhouse gas laden atmosphere absorbs and re-emits radiation from the earth with only a portion of it escaping to earth. 

Consider the simplified drawing below. 

Picture: Global “Greenhouse” Warming

This diagram breaks down the radiative physics behind global warming against a layered atmospheric backdrop.

• The sun projects solar radiation toward Earth, with yellow arrows indicating that roughly 29.5% of incoming sunlight is reflected straight back into space due to albedo.
• Energy from the sun is also directly absorbed by GHGs in the atmosphere. 
• The Earth absorbs the remaining energy and re-emits it upward as thermal radiation, represented by a branching network of orange arrows showing absorbed and re-emitted infrared (IR) energy.
• Approximately 60% of Earth’s thermal radiation eventually escapes into outer space through the thinner, colder upper layers of the atmosphere.

The top section of the image details the specific thermodynamic mechanism driven by greenhouse gases.

• As concentrations of CO₂ and other greenhouse gases increase, they extend into higher atmospheric altitudes.
• This pushes the IR “escape boundary” upward into colder air layers;
• because less heat radiates into space at these lower temperatures, the Earth’s surface and lower atmosphere must experience a temperature (T) increase to balance the total solar energy absorbed.

CO2 (mainly) is the cause of global warming.

• It’s sometimes called the “radiative forcing agent”.
• It’s the primary driver; the causal factor. 

The core climate indicator that reflects this warming is of course temperature and this rise in temperature affects the earth in various ways

Let’s explore the CO2 and Temperature data that scientists collect and track and then provide examples of what these cause on earth (the evidence).

Global Warming Bathtub Analogy

Global warming is fundamentally an energy balance problem best understood as a bathtub whose drain is slowly being clogged, forcing the water level to rise until pressure restores the balance.

Consider the bathtub drawing below where we have a flow of water coming in through the faucet and flowing out through the drain. 

Picture: Bathtub Analogy to Global Warming 

There are two equations at play here; Torricelli’s Law

Qout = Adrain√(2gh)

where

• Qout : Outflow rate (volumetric fluid discharge)
• Adrain: Cross-sectional area of the drain
• g: Acceleration due to gravity
• h: Height of the water column (hydrostatic head)

and the Stefan-Boltzmann Equation

Eout = τεσT⁴

where

• Eout: Outgoing longwave thermal radiation flux
• τ: Atmospheric transmissivity (we said this was about 60%)
• ε: Surface emissivity of the Earth (we assume 1)
• σ: Stefan-Boltzmann constant
• T: Absolute surface temperature

Picture: Bathtub Analogy to Global Warming  – Table

The analogy of the draining bathtub to a warming Earth goes as follows:

Step_1: Steady-State Equilibrium (Temperature and Height analogy)

• Bathtub: Water enters at Qin  and exits through drain area Adrain  at rate Qout  = Adrain √(2gh).
• Inflow equals outflow keeping water level h completely stable.
• Earth: Solar energy enters at Ein  and exits through atmospheric transmissivity τ at rate Eout = τεσT⁴.
• Energy input equals radiation output, keeping surface temperature T completely stable.

Step_2: Restricting Outflow Capacity (Transmittivity τ  and Adrain analogy )

• Bathtub: A partial clog reduces the drain area (Adrain  ↓). With less area to exit,  Qout  drops below Qin. 
• Earth: Greenhouse gases accumulate, lowering atmospheric transmissivity ( τ  ↓ ).
• With less infrared light passing through directly to space, Eout drops below Ein.

Step_3: Accumulating Mass and Energy (Qin > Qout; Ein > Eout )

• Bathtub: Because Qin > Qout , water has nowhere to go and begins accumulating in the tub (h starts rising ↑).
• Earth: Because Ein > Eout , thermal energy has nowhere to go and begins accumulating in the climate system.

Step_4: Building Pressure to Force Outflow (h ↑ ; T ↑)

• Bathtub: Accumulated water causes water height h to rise.
• Under Torricelli’s Law, a higher water level h creates greater hydrostatic head pressure, pushing water through the constricted drain Adrain faster.
• Earth: Accumulated heat causes surface temperature T to rise.
• Under the Stefan-Boltzmann Law, a higher temperature T creates stronger thermal emission “pressure” (T⁴ ↑ ), pushing infrared energy through the “restricted” atmosphere τ faster.

Step_5: Re-establishing Equilibrium at a Hotter Baseline (h2 > h1 ;  T2 > T1)

• Bathtub: The water level stops rising once h reaches a high enough level (h2) where hydrostatic pressure forces Qout to match Qin again: Qout = Adrain2sqrt√(2gh2)
• Earth: Temperature stops rising once T reaches a high enough level (T2) where thermal pressure T⁴  forces Eout  to match Ein again: Qin = τ2 epsilon sigma T2⁴

The temperature increase from T1 to T2 is global warming; the exact physical equivalent of a bathtub needing a higher water level (h2) to maintain flow balance through a clogged drain.

CO2 Data

How and Where is it Measured? Is it Accurate?

Atmospheric carbon dioxide CO₂ is continuously monitored across a global network of remote, high-altitude observatories (for example, Hawaii’s Mauna Loa Observatory at 3,400 meters elevation) using optical spectroscopy instruments that measure the exact amount of infrared light absorbed by clean, dry air samples.

• Relying on Mauna Loa’s record alone is fully indicative of planetary climate trends because CO₂ persists in the atmosphere for centuries, giving global winds ample time to thoroughly mix the gas across the globe within a single year.
• Positioned far from major industrial pollution, Mauna Loa samples pristine, well-mixed air from the upper troposphere that stays within 1 to 2 parts per million (less than 0.5%) of the global ocean-and-land average, while rigorous automated filtering routinely strips out any localized volcanic or plant emissions.
• As a result, Mauna Loa’s data curve functions as a very precise proxy for the entire planet, capturing both the Earth’s natural seasonal biosphere cycles and its long-term atmospheric trajectory.

Historical CO₂ Trends

The graph below displays the Keeling Curve ; the direct measurement of atmospheric carbon dioxide taken at Hawaii’s Mauna Loa Observatory since 1958.

Graph: Historical CO₂ at Mauna Loa Observatory

• The “Seasonal Sawtooth”: The fine red zig-zag captures Earth’s seasonal respiration. CO₂ levels dip each spring and summer as vast Northern Hemisphere forests photosynthesize and draw down carbon, then peak in winter and early spring as vegetation decays and releases it back.
• Accelerating Velocity: The trend line isn’t just going up—it is steepening. In the 1960s, atmospheric CO₂ increased by roughly 0.9 ppm per year, whereas the current growth rate routinely exceeds 2.0 to 2.5 ppm per year.
• Major Baseline Shift: Reaching 427.55 ppm in August 2026 represents a >52% increase over the ~280 ppm pre-industrial baseline, pushing atmospheric concentrations into territory unprecedented in human history.
• Institutional Benchmark: Maintained through combined data from the Scripps Institution of Oceanography and NOAA, this record serves as the global baseline for tracking human-driven greenhouse gas accumulation.

The NASA graph below tracks atmospheric carbon dioxide CO₂ levels over the past 800,000 years, contrasting historical natural cycles with modern concentrations.

Graph: Historical CO₂ Levels over the past 800,000 years

• Data Sources: Ancient ice core data (yellow) with direct modern instrumental measurements (red) are used to measure CO₂. 
• Historical Baseline: Shows natural fluctuations bounded between about 180 ppm and 300 ppm across eight glacial/interglacial cycles over 800,000 years.
• The 300 ppm Threshold: Features a dashed reference line at 300 ppm to highlight that atmospheric CO₂ never exceeded this level for millennia prior to the 20th century.
• Modern Surge: Demonstrates a steep, nearly vertical rise beginning around 1911, climbing past 315 ppm in 1958 to over 420 ppm today

Temperature

How/Where is Temperature measured?

Global surface temperature is measured through a worldwide network of thousands of land weather stations, ocean buoys, research ships, and satellite radiometers.

• To standardize these diverse inputs, scientists convert raw readings into temperature anomalies (deviations from a long-term local baseline) which neutralizes geographic and elevation differences.

These measurements are exceptionally reliable:

• automated processing algorithms rigorously correct for non-climatic biases, such as station relocations, changing measurement times, or urban heat island effects.
• Independent international research groups (including NASA, NOAA, the European Union’s Copernicus, and Berkeley Earth) apply different processing methodologies to the raw data and arrive at virtually identical global warming trends within fractions of a degree

NOAA Temperature Departure (Anomaly) Data

The below NOAA anomaly (temperature departure) chart shows the global surface temperature outcome of rising atmospheric CO₂ levels.

Graph: NOAA Anomaly (Temperature Departure) Data

• A temperature departure is calculated by subtracting a location’s long-term historical average for a given month from its actual recorded temperature.
• These local differences are then area-weighted and averaged across the globe to produce the overall temperature anomaly.
• The Blue-to-Red Shift: Visualizes a stark regime change from a cooler 19th and early-20th century (dominated by blue bars below the 1901–2000 average) to an unbroken, multi-decade sequence of above-average temperatures beginning in the late 1970s.
• Steepening Modern Spike: The last decade (2015–2026) displays an unprecedented cluster of extreme August anomalies, with temperatures spiking sharply to nearly +1.3°C (+2.3°F) above the 20th-century baseline.
• Baseline Nuance: Because NOAA uses the 20th-century average (1901–2000) for its zero reference line, total warming compared to true pre-industrial levels (1850–1900) is actually an additional ~0.2°C to 0.3°C higher than depicted here.
• Coupled Warming: By integrating both land and sea surface data, the chart highlights that thermal inertia across global oceans is being systematically overcome alongside land surface warming.

But The Temperature Change is So Small. How could it possibly do any damage?

https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature

While NOAA’s chart displays a 1.32°C anomaly based on a 20th-century average (1901–2000), adjusting to the cooler pre-industrial baseline (1850–1900) used by the IPCC brings total warming right to the standard 1.5°C benchmark.

But so What? Since pre-industrial times our Earth’s temperature has risen 1.5 C but an average person in the United States experiences an outdoor annual temperature range of 30°F to 90°F (-1°C to 32°C) across changing seasons. 

This amount sounds trivial because in most human contexts, we experience a much wider range of temperature and do just fine.  

• Equating short-term local weather swings with the global climate baseline is the central disconnect in climate communication.
• We need to come back to our energy balance to understand this. 

Recall our energy balance (see picture below) from the “Earth Average Energy Balance” section.  

Picture: Earth Average Energy Balance (2015 – 2023)

Today (latest data at least) earth emits about 398 Watts per square meter (W/m²) emitted by the earth and the Stefan-Boltzmann equation (see “Stefan-Boltzmann Equation” section) tells us this is equivalent to a blackbody radiator at 16.3 C.

• E = εσT⁴  where σ = Stefan-Boltzmann constant =   5.670 × 10-8 W/m²/K⁴, T = temperature in Kelvin (C + 273.15 = K) and ε = emissivity as a percent efficiency factor assumed to be 100%
• For E = 398,  T = 16.3 C

The pre-industrial baseline for radiation emitted from earth is about 390 W/m². 

So in terms of the Earth’s energy balance, driving a 1.5°C total surface warming requires trapping an extra 8 W/m² ( 398 – 390 = 8 W/m²) of thermal radiation continuously across every square meter of Earth.

• That accumulated surplus equals roughly 4,000 Terawatts of excess power; over 200 times the energy output of all human civilization combined, or
• physically equivalent to leaving an 80-watt heat lamp running non-stop over every single 10-by-10-foot patch of land and ocean on the planet.

That vast energy surplus doesn’t sit idle.

Looking at the energy diagram we have 82 W/m² of Latent Heat flow, much of this extra heat acts as a massive contributor to global evaporation, forcing oceans to boil off water vapor at unprecedented rates.

This supercharges storm systems, dries out soils into mega-droughts, and bakes the oceans.

A 1.5C warming shift is not a mild change in weather; it is the signature of trillions of watts of raw energy permanently altering the Earth system.

A useful analogy is the core temperature of the human body. 

• A healthy human maintains a tightly regulated core temperature near 98.6°F (37°C).
• Similarly, Earth’s climate relies on a delicate energy balance between incoming solar radiation and outgoing heat to maintain a stable planetary baseline.
• External Fluctuation vs. Core Shift: You can comfortably walk from a 70°F air-conditioned room into a 95°F afternoon because your body actively regulates its core.
• However, if your internal core temperature rises by just 2°F to 100.6°F, you have a fever.
• Earth easily handles 20°F local daily weather swings, but a 2°F rise in its total global average represents a planetary “fever”.
• Cascading Symptoms: A fever isn’t just “feeling warmer”; it triggers systemic stress, inflammation, and organ strain.
• Likewise, a small upward shift in global baseline temperature triggers cascading symptoms across planetary systems: jet stream destabilization, ocean heatwaves, and accelerated ice sheet collapse

Average versus Extremes

Another way to think of an increase in average temperature is to think of what that means regarding the extremes.  

The image below shows two “bell” curves mapping out daily temperatures (normal probability distributions).

Picture: Global Warming Shift Shown on Two Normal Distribution Curves

The second curve is identical to the first, just slid to the right, and represents a hypothetical increase in average global temperatures.

When thinking about global warming, the average temperature isn’t what matters—it’s the extreme events.

• A few extra degrees on a normal day is barely noticeable, but those same extra degrees added to an already dangerous heatwave turn it into a disaster.

Evidence

I encourage you to read more about each of these using the links provided below

References  

• https://science.nasa.gov/climate-change/evidence/ ; Google Gemini
• https://www.climate.gov/climatedashboard
• Google Gemini

Beyond rising atmospheric CO₂ levels and global surface temperatures, climate scientists track key empirical indicators across the ocean, ice sheets, and biosphere to measure accelerating planetary warming:

Cryosphere Breakdown (Ice & Snow)

• Shrinking Ice Sheets: Satellite observations hosted on NASA’s Sea Level Change Portal show Greenland losing ~260 billion metric tons of ice per year and Antarctica losing ~100 billion metric tons annually, directly driving sea level rise.
• Glacial Retreat: The US Geological Survey (USGS) documents accelerated mountain glacier loss worldwide, which alters regional hydrology and threatens freshwater supplies.
• Permafrost Thaw & Sea Ice Decline: Reports from the US EPA Climate Change Indicators track steady declines in Arctic sea ice extent along with rising permafrost ground temperatures across northern latitudes, which threatens northern infrastructure and releases trapped methane.

Ocean Heating & Chemical Shifts

• Record Ocean Heat Content: Data from NOAA Climate.gov indicate oceans store over 90% of the excess heat trapped in Earth’s climate system, fueling severe marine heatwaves and widespread coral bleaching.
• Accelerating Sea Level Rise: Measurements on NASA Earth’s Sea Level Portal record over 100 millimeters of global sea height variation since satellite tracking began in 1993, driven by thermal expansion of warming seawater and melting land ice.
• Ocean Acidification: Monitoring by the NOAA Ocean Acidification Program tracks declining surface ocean pH levels as seawater absorbs excess atmospheric carbon dioxide, disrupting marine food webs and calcifying organisms.

Atmospheric & Extremes Indicators

• Accelerating Global Surface Temperatures: Historical analysis from NOAA National Centers for Environmental Information shows global warming has accelerated to more than three times its 1850–1975 rate over recent decades, making the past decade the warmest on record.
• Extreme Weather Frequency: The US EPA Climate Indicators Dashboard details measurable increases in heatwave frequency, heavy precipitation events, prolonged mega-droughts, and lengthening wildfire seasons.

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