Hope or fear: which is the better motivator?

I receive a daily list of climate change news items from the world's media using a service called 'climate list' (worth joining if you're interested). Today I was struck by two headlines:

The first:
Effective response to climate change depends on hope, not fear
(anthropocenemagazine.org)

The second:
Are There Zombie Viruses In The Thawing Permafrost?
​(npr.org)

The moral in very British terms is hope for sunny weather but always carry a brolly.