Climate evidence, carbon cycling and temperature effects

What you’ll learn

• Evaluate climate evidence and model predictions.
• Explain carbon management and its trade-offs.
• Calculate Q10 and connect temperature to biological responses.

Understand the idea

Greenhouse gases absorb and re-emit outgoing infrared radiation, reducing net energy loss to space and warming the lower atmosphere and surface. Human activities alter their concentrations. Direct temperature and atmospheric gas records can be compared with proxy evidence: pollen assemblages indicate past vegetation and climate, while tree rings record growth influenced by temperature and water availability. Several independent lines of evidence are more persuasive than one correlation; calibration, dating and confounding factors matter.

Photosynthesis removes atmospheric carbon dioxide; respiration, decomposition and combustion return it. Reforestation can increase carbon storage, but permanence, land use and ecosystem effects must be considered. Biofuels may reduce net fossil-carbon input only when regrowth and the whole production chain are included. Climate models apply physical principles to data; uncertainty in future emissions, feedbacks and parameters creates a range of projections rather than making all projections meaningless. Separate evidence from the interests or values influencing proposed policies.

Temperature affects enzyme-controlled development, distribution and seasonal timing. Within a suitable range, greater kinetic energy can increase rates; above an optimum, enzyme or cellular damage can reduce them. Q10 compares rates ten degrees apart and should not be treated as constant across all temperatures. Changes in rainfall and timing can separate food availability from breeding demand. A development investigation needs comparable organisms, controlled conditions, repeats and ethical treatment; non-invasive plant measurements can answer many questions.

Key formulae

$$Q_{10}=\frac{R_{T+10}}{R_T}$$

$$Q_{10}=\left(\frac{R_2}{R_1}\right)^{10/(T_2-T_1)}$$

Worked example

An organism's development rate is $0.08\,\mathrm{day^{-1}}$ at $15^\circ\mathrm C$ and $0.16\,\mathrm{day^{-1}}$ at $25^\circ\mathrm C$. Calculate Q10 and assess a prediction for $45^\circ\mathrm C$.

1. The temperatures differ by $10^\circ\mathrm C$.
2. Calculate $Q_{10}=0.16/0.08=2$.
3. Extrapolating the same factor to much higher temperature ignores possible enzyme denaturation, stress and mortality.

Answer: Q10 is 2 for the measured interval; the data alone do not justify extrapolation to 45 °C.