Equus has never experienced hippogenic climate change, since little ponies have never relied heavily on burning fossil fuels.
During the droughts of the Dark Age, large amounts of carbon sequestering vegetation and algae died off, releasing CO2. However, any greenhouse effect was offset by the increased surface reflectivity of the now-exposed vast dry salt flats and the removal of heat capacity stored in ocean water, resulting in a slight drop in global average temperatures.
With the return of the oceans and more frequent rain, new growth of terrestrial plants and large blooms of marine algae have once again sequestered most of this excess CO2. Heating of ocean water and increased average humidity have again similarly offset this reduction in greenhouse gas, resulting in a slight rise in global average temperatures back to precatastrophic levels.