Last year was a remarkable year for renewables and renewable energy investment. So good, in fact, that investment in renewable generation during 2015 was twice as high as investments in new coal- and gas-fired power plants. That's just one of the snippets of good news from a new report from the United Nation's Environmental Program entitled Global Trends in Renewable Energy Investment 2016. Another eyebrow-raising factoid: Renewables represented 53.6 percent of the gigawatt capacity of all energy generation technologies installed in 2015 — the first time renewables had ever represented a majority of newly installed capacity.

But the truly good news is that this appears to be a long-term trend.

Tracking year-on-year renewable energy investment shows a rise from $73 billion in 2005 to a whopping $286 billion in 2015, which represents a growth of nearly 300 percent. This figure is, of course, even more impressive when you consider that the price of solar panels and wind turbines keeps on dropping, so every dollar spent in 2015 buys a whole lot more than it did back in 2005.

Now, we should be careful not to get too carried away. Investment in 2012, 2013 and 2014 actually dipped, and shifts in economic headwinds or policy decisions can have a significant impact on the short-term prospects of clean energy growth. So just because last year was a banner year does not mean that every year moving forward will break similar records. Indeed, the report points out that investment in European renewable energy, for example, slumped thanks to fickle government policy and a rapid scaling back of subsidies that had proved more popular than expected.

But short-term policy volatility aside, it really is beginning to look like a fundamental transition in energy generation is underway on a global level. Given that the Paris Climate Agreement has sent a signal to investors that almost every government in the world is committed to a low carbon transition, we can expect increased policy certainty that should drive a continued growth in investment. And as renewables get less and less subsidy dependent, their vulnerability to policy shenanigans will also be reduced.

No wonder investors are beginning to see the economic case for divesting from fossil fuels and investing in renewables instead. The only question now is not whether this transition will happen, but whether it will happen fast enough to curtail the worst impacts of global climate change. Here, sadly, the jury is still out. In a press release announcing the launch of the new UNEP report, Prof. Dr. Udo Steffens, President of the Frankfurt School of Finance & Management, pointed to low commodity prices as a potential incentive for governments to keep relying on fossil fuels:

“Despite the ambitious signals from COP 21 in Paris and the growing capacity of new installed renewable energy, there is still a long way to go. Coal-fired power stations and other conventional power plants have long lifetimes. Without further policy interventions, climate altering emissions of carbon dioxide will increase for at least another decade. [...] The commitments made by all nations at the Paris climate summit in December, echoing statements from last year's G7 summit, require a very low- or no-carbon electricity system.”

So, in summary, 2015 was a great year for renewables. But we're going to need a whole lot more great years if we're going to pull this off.