What was the atmosphere like during the Jurassic Period in comparison to today's?
there is evidence that the atmosphere was much more humid, with higher levels of Carbon Dioxide and likely more cloud cover.
During the Jurassic period there is evidence that there was lush forests. These forests were made of fern trees as a dominate life form. Ferns require a high level of humidity and water. This indicates that the atmosphere had higher levels of Carbon Dioxide than in the present atmosphere. Also the fossils evidence indicates that the atmosphere had higher levels of humidity than the present.
the size of the dinosaurs, giant snakes, huge crocodiles indicate that the climate was more uniform than the present. These organisms are cold blooded and could not reach their gigantic size in a climate with cold winters. and extremely hod summers. Large reptiles are presently only found in tropical climates near the equator. The climate throughout the earth may have been at least semi tropical which would require a cloud cover, that would equalize the temperature throughout the earth.