Here’s a funny fact: it is estimated that in 2020 space crafts will have roughly the same environmental impact as the total electricity consumption of the US.

Abolishing space travel entirely will have the same effect as replacing just under 15% of electricity worldwide by an ideal green source (no emission at all). By comparison, the total amount of electricity we get from renewable (not necessarily green!) energy sources is in the low 20% percents.

Sources:
“propellant burned by rockets… could represent a net additional heatin… on the atmosphere comparable to all of aviation”: http://www.aerospace.org/crosslinkmag/summer2011/rocket-soot-emissions-and-climate-change/
“Worldwide, flights produced 705 million tonnes of CO2 in 2013”: http://www.atag.org/facts-and-figures.html
“US: 5270, World: 32310”: https://www.eia.gov/cfapps/ipdbproject/iedindex3.cfm?tid=90&pid=44&aid=8&cid=regions&syid=2008&eyid=2012&unit=MMTCD
“we could switch all electricity to unicorn dust… and still only make a reduction of around 15% of total emission”: https://westergaard.eu/2015/05/reality-check-elon-musk-and-manipulation/
“about 21% of world electricity generation was from renewable energy in 2011”: http://www.eia.gov/tools/faqs/faq.cfm?id=527&t=1