Have the media lost interest? Is it a question of chronic political fatigue? Are our brains simply not wired to think long-term?
The BBC World Service's The Inquiry hears from four expert witnesses.
Max Boykoff founded the Media Climate Change Observatory a decade ago.
"We monitor 50 sources around the world across 25 countries on six continents. We seek to put our fingers on the pulse of the ebbs and flows of coverage of climate change over time, month to month.
"It's not an exhaustive reading of all media accounts everywhere around the globe across all platforms, but rather is a way to get us talking productively.
"In 2004 there were relatively low levels of coverage. Around 2006, into 2007 there was an uptick. There was a high water mark in 2009 [at the time of the UN Climate Change Conference in Copenhagen].
"From that high water mark to 2014, coverage has dropped: 36% globally; 26% in the US; and as much as 55% in the UK.
"Within the last year here in the United States, National Public Radio reduced its environment reporting team from three to one reporter.
"We see examples of this unfolding quite regularly. There's certainly newsroom pressures. There's shrinking time to deadline, there's reduced resources to cover complex issues such as climate change that require a certain level of investigation, a certain level of familiarity with the contours and the nuances of the topics."
Jennifer Morgan is the Global Director of the climate change programme at the World Resources Institute.
"Copenhagen was supposed to be the moment when over 190 countries came together and agreed a new legally binding agreement to address climate change. It was very much a great excitement and anticipation of trying to finally get a global agreement after the Kyoto years.
"I remember walking in with a colleague of mine, and saying 'Okay, we have to do it.  We have to get this done, these moments don't happen very often'.
"But it soon became clear that negotiations weren't going to plan:
"In the middle of the second week normally what happens is the options start to get narrowed down, and you can see the package emerging. That wasn't happening, and that's when we all started to get very concerned."
China's chief negotiator was barred by security for the first few days, sessions were routinely suspended in the name of finishing on time, developing countries said they were ignored, and the EU was missing from a final meeting where a last-minute, non-binding deal was drawn up.
"It was terrible. [We felt] an exhausted defeat, just a deep fatigue, particularly from the European side, of just wanting to take a break. The personal sacrifice - it sounds crazy - but believing and trying to make something happen, I think it was a trauma, just to put so much blood, sweat and tears into it.
"Right after Copenhagen, there was a sense that there needed to be a bit of a time out on the world leaders' side of things. So it definitely went into a very low level of attention for a few years. The relationships of some of the Heads of State after Copenhagen were quite strained.
"Even months after, it was almost like [they] had been being psychologically burned by this.
"That's had a real impact on the willingness of these individuals to stay engaged."
Environmental psychologist Robert Gifford researches why even those who accept a link between human behaviour and climate change are reluctant to act.
"Our brain physically hasn't developed much for about 30,000 years. At that time we were mostly wandering around on the Savannah, and our main concerns were very immediate: feeding ourselves right now, worrying about anybody who might try to take our territory. There was very little thinking about what might happen in five years, 10 years, or 100km away.
"We still have this same brain. Obviously we're capable of planning, but the kind of default is to stick into the here and now, which is not very good for thinking about climate change, which is a problem that, for many people, is more in the future and farther away, or at least we think it is.
"[And] as any advertiser knows, if you don't change your message people will just tune out. And so environmental numbness is 'yes, I've heard that message before'. We're always open to new messages, and paying more attention to new messages. So if governments or policymakers repeat the same message too often, people just tune out after a while."
We also tend to tune out when we feel helpless:
The Inquiry is broadcast on the BBC World Service on Tuesdays from 13:05 GMT
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"'What can I do about this global problem? I'm just one person, and there's 7+ billion people on the planet. I just don't have much control over this, so therefore I'm not going to do much about it, because my contribution, even if I did everything, wouldn't make much difference.'
"Most of us who are trying to do something about this have realised, for example, that the polar bear metaphor is not a great one. Yes, we have some sympathy for this poor polar bear, but it's not close enough to our own lives.
"Uncertainty is a really big problem. We've learned in my own laboratory from experimental evidence that when people feel a bit uncertain about an environmental problem - if the future temperature might vary from a half a degree increase to a one and a half degrees increase - people will say 'well, it's probably only going to be a half a degree increase, so I'll keep flying to some tropical place'.
"It's a natural human tendency to interpret information in a way that suits our personal interests.
Joe Smith teaches geography at the Open University and argues the narrative around climate science must evolve.
"I'm not sure that people need to engage with climate change at all. It's more or less unreportable if you just describe it on the page.  It's complex, interdisciplinary, the findings drip out over time, and the boundary between science and policy and politics is a very messy one. It's a real challenge for the media.
"The idea that we will mobilise any more people with fear messaging is wrong.  I think we've knocked at the door of everyone that might respond to such a thing, but you've also got to ask whether it's an accurate way of telling the science.  I think it is more respectful to the nature of the science to say that it's one of humanity's most ambitious questions.
"There was a tactical wrong turning in suggesting that by insisting that the debate is over, we can move onto the action. It somehow implied that the science was complete, and that, of course, left lots of space for those people who have arguments about the actions on climate change to stand in the way of us having a proper public conversation about those actions because they were able to pick apart minor details in the science.
"It's not just that climate science isn't finished, it's actually unfinishable.
"The rest of science - particle physics, cosmology - is allowed to be rather saucy. I would love to get to the point where we allow climate change science to simply be interesting, enchanting even, as fascinating as any area of science because it's a hugely ambitious and compelling mission.
"If you want to talk to a business person, you talk about energy security for their business or energy security for their nation.  If you want to talk to a parent at the school gate, you talk to them about the health of their child, their experience of the trip to school - wouldn't they be happier walking and cycling?
"Talking about climate change doesn't have to involve 'talking about climate change' to lead us to some really substantial actions.
"We don't need to wear a climate change t-shirt."
The Inquiry is broadcast on the BBC World Service on Tuesdays from 13:05 GMT. Listen online or download the podcast.
Since there is a consensus amongst the majority of the world's scientists that temperatures are rising - most likely driven by human behaviour - why does climate change coverage seem to be drying up?