Concordia University PHYS 273 LESSON 11 1)Burning fossil fuels The last time atmospheric CO2 concentrations were as high as they are now was… The source of the increase in atmospheric CO2 is The ratio of different types of carbon in the atmosphere tells us Greenhouse gases Which of the following is a statement about the climate? In which of the following regions has food production been affected the most by climate change? T or F: The Earth is warming The Earth loses energy by The Earth is able to reach an energy balance because Greenhouse gases are gases that The last 3-4 decades have been …   T or F: There are global regions which have not been affected by climate change T or F: Without humans there would be no greenhouse effect Global mean sea levels have been steadily rising since 1900