Statement, Tutorial
How scientists calculate climate change
- Historical Foundation
- Wilhelm Bjerknes linked heat, water, and air flow via formulas in the late 19th century, establishing the basis for the first atmospheric computer models fifty years later.
- Modern climate computers are approximately 25 trillion times faster than the original atmospheric models.
- Model Mechanics and Structure
- Scientists divide the atmosphere into hundreds of thousands of grid cells; for instance, the Met Office model utilizes stacks of 85 cells high.
- Weather forecasting calculates atmospheric snapshots for immediate prediction, whereas climate models simulate behavior over years or decades.
- Early models tested scenarios such as doubling carbon dioxide levels to illustrate potential 21st-century greenhouse warming.
- Technical Limitations and Discrepancies
- Grid cells can span hundreds of kilometers, causing models to struggle capturing small-scale details like cloud cover.
- Clouds have dual effects on temperature by either trapping sunlight (warming) or reflecting it (cooling), processes too small to model precisely.
- Modelers must use "rules of thumb" for cloud behavior, leading to divergent assumptions where some models run "hot" (higher warming) and others run "cold."
- Comparisons of 1970s models against 2000s data show that most successfully predicted actual observed warming within their error bars.
- Economic Scenarios and Policy Projections
- Models cannot predict human behavior, requiring scientists to couple physical climate models with economic models to assess policy impacts.
- A 2013 study compared four scenarios: continued coal use, fossil fuels with some renewables, high renewable uptake, and heavy carbon capture/biofuels.
- Results indicate only stringent climate policies can keep global temperature rise "well under two degrees" above pre-industrial levels as per the Paris Agreement.
- Current emission reduction trajectories are insufficient to assure staying below 2 degrees, let alone the 1.5-degree target.
- Conclusion and Future Outlook
- While models cannot fully represent all intricate Earth processes, they remain the primary tool for quantifying the damage of increased carbon dioxide.
- The ultimate solution to climate change relies on human decisions informed by these models rather than the models themselves.