Re: NASA chief touts deep space exploration: We can only survive if we Um, no. The Sahara is shrinking. Increased CO2 means that plants lose less water through transpiration, allowing them to move into areas formerly too dry for them. Global warming also increases rainfall. For example, El Nino produces floods, and la Nina produces droughts. Past temperatures are sometimes estimated by using rainfall as proxy. The planet's largest and driest desert is in Antarctica, not Africa.