1. It is said that the average temperature of the atmosphere has risen by 1.5 C over the last 100 years. How do we know this? There must be sophisticated methods of measuring the temperature now, but how was average temperature measured 100 years ago?
2. Apparently the CO2 level is now around 400ppm. Is this a global average or is this a uniform figure ie is the CO2 level in the UK the same as that in India and of that over the centre of the Pacific? If it is not uniform is it reliable to compare levels now with levels inferred from CO2 trapped only in Antarctic ice? And would CO2 in this air be dissolved into the ice with time, thus giving falsely low readings?
3. If a country is told to cut its CO2 levels by X%, how does anyone know if they have done this or not? How are a country's emissions measured (or calculated)?
Please help me understand!