Final answer:
The CO₂ trend in the Earth's atmosphere is an upward trajectory from pre-industrial levels of around 280 ppm to current levels over 400 ppm, primarily due to fossil fuel combustion. This increase in CO₂, causing the enhanced greenhouse effect, corresponds with a rise in global average surface temperatures by approximately 1°C since 1950.
Step-by-step explanation:
The CO₂ trend refers to the increasing concentration of carbon dioxide in Earth's atmosphere, which has escalated from about 280 parts per million (ppm) before the industrial revolution to over 400 ppm now. This rise in CO₂ levels, primarily due to the combustion of fossil fuels, leads to the enhanced greenhouse effect, resulting in increased global average surface temperatures. Historically, the Earth's climate has experienced natural fluctuations, with CO₂ levels cycling between 180 - 300 ppm over geological times.
However, the current trend of rapid increase is unprecedented in this time scale. Since 1950, there has been a clear upward trajectory in the atmospheric CO₂, from about 280 ppm to levels significantly above 300 ppm, which has been accompanied by an increase in the Earth's average surface temperature by approximately 1°C. This relationship is direct; as atmospheric CO₂ concentrations rise, the global surface temperatures tend to rise in correspondence.
Moreover, the temperature rise is not homogenous over time. For instance, the so-called 'global warming hiatus' suggests short-term countertrends that could mask the longer-term warming trends. But these short-term fluctuations have not altered the overall rising trends of both CO₂ and surface temperature.