Gemini 2.5 reasoning.

 What sort of field physics experiment would be required to quantify the actual effect of carbon dioxide on earth warming

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Okay, let's break down what kind of physics-based field experiments are used to understand and quantify the warming effect of carbon dioxide (CO2).

It's crucial to understand upfront that isolating the exact warming effect of CO2 alone in a single, simple field experiment covering the entire, complex Earth system is practically impossible. The climate is influenced by many interacting factors (water vapor, clouds, aerosols, ocean currents, solar variations, other greenhouse gases).

However, scientists use a combination of sophisticated field measurements, remote sensing, and laboratory physics, which together allow them to quantify CO2's role. Here are the key types of physics-based field observations and measurements involved:

Atmospheric Spectroscopy (Measuring Absorption and Emission):

Principle: CO2 molecules absorb and re-emit infrared (longwave) radiation at specific wavelengths. This is the fundamental mechanism of the greenhouse effect.   

Field Experiment/Measurement:

Ground-Based Fourier Transform Infrared Spectrometers (FTIR): Instruments located at monitoring stations around the world (like those in the Baseline Surface Radiation Network - BSRN, or the Total Carbon Column Observing Network - TCCON) continuously measure the spectrum of infrared radiation coming down from the atmosphere towards the surface (downwelling longwave radiation). By analyzing the intensity of radiation at the specific wavelengths absorbed and emitted by CO2, scientists can directly measure the increase in radiation reaching the surface due to CO2 (and other greenhouse gases). Comparing measurements over years, as CO2 concentrations rise, shows a quantifiable increase in this downwelling radiation, consistent with theoretical predictions.

Satellite-Based Spectrometers: Instruments on satellites (like AIRS on Aqua, IASI on MetOp, CrIS on Suomi NPP/JPSS) look down and measure the spectrum of infrared radiation leaving the Earth's atmosphere for space (outgoing longwave radiation). As CO2 concentrations increase, these instruments detect less radiation escaping to space specifically at the wavelengths CO2 absorbs. This provides direct, global evidence that CO2 is trapping more heat.   

Radiative Flux Measurements (Measuring Energy Flow):

Principle: The greenhouse effect changes the overall energy balance of the Earth. Increased CO2 reduces the amount of heat escaping to space and increases the amount radiated back towards the surface.   

Field Experiment/Measurement:

Surface Radiation Budget Stations (e.g., BSRN): These sites use instruments like pyrgeometers (measuring total infrared radiation) and pyranometers (measuring solar radiation) to carefully monitor the upward and downward flows of both shortwave (solar) and longwave (infrared) radiation. Long-term measurements show an increase in downwelling longwave radiation at the surface that correlates with rising greenhouse gas concentrations, providing a measure of the enhanced greenhouse forcing.

Satellite Measurements of Earth's Energy Imbalance (EEI): Satellites like CERES (Clouds and the Earth's Radiant Energy System) measure the difference between incoming solar radiation absorbed by Earth and the outgoing longwave radiation emitted to space. An increasing positive imbalance (more energy coming in/staying in than leaving) is observed, consistent with the heat being trapped by increasing greenhouse gases. While this measures the total imbalance, analysis combined with spectral data helps attribute portions of it to specific factors like CO2.   

Atmospheric Composition Monitoring:

Principle: To quantify the effect of CO2, you need precise measurements of how much CO2 is actually in the atmosphere, where it is, and how it's changing.

Field Experiment/Measurement:

Global Monitoring Networks: Ground-based stations (like the iconic Mauna Loa Observatory), ships, and aircraft collect air samples that are precisely analyzed for CO2 concentrations (e.g., using non-dispersive infrared sensors or cavity ring-down spectroscopy). This provides the data showing the steady rise in global CO2 levels. Vertical profiling using aircraft or balloons helps understand CO2 distribution with altitude.

Isotopic Analysis: Measuring the ratios of carbon isotopes (¹³C/¹²C and ¹⁴C) in atmospheric CO2 helps confirm that the increase is primarily due to burning fossil fuels (which have a distinct isotopic signature). While not directly measuring temperature, this confirms the source of the added CO2 being measured by the radiative experiments.

Synthesizing the Quantification:

No single experiment listed above alone definitively quantifies the exact degree of warming solely from CO2 across the whole planet in isolation from feedbacks. Instead:

Lab measurements establish the fundamental absorption properties of CO2.   

Field spectroscopic measurements (ground and satellite) directly observe CO2 absorbing and emitting radiation in the real atmosphere, confirming less heat escapes and more returns to the surface at CO2-specific wavelengths. These changes are quantifiable over time.   

Field radiative flux measurements quantify the total change in the Earth's energy balance at the surface and top of the atmosphere.

Atmospheric composition measurements track the increase in CO2, linking it to the observed radiative changes.

Climate models, constrained and validated by these physical measurements, are then used to disentangle the contributions of CO2 from other factors (like water vapor feedback, clouds, aerosols) and estimate the resulting global temperature change (climate sensitivity).

Therefore, quantifying the actual effect of CO2 relies on the convergence of evidence from these diverse, physics-based field measurements combined with fundamental physics and sophisticated modeling. The field experiments provide the real-world data demonstrating the enhanced trapping of heat consistent with the measured increase in atmospheric CO2.   

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This should have been done a long time ago.  However, there is the tiny problem that it would show zero impact of the imaginary 'greenhouse gases'.  Therefore, never done.