One of the cruel ironies of climate change is that the poor countries that have contributed the least to the problem are expected to get hit the hardest.

That's why, in recent years, many of the world's wealthier nations — including the United States, Germany, Britain, and Japan — have promised billions of dollars in aid to help developing countries adapt to the impacts of global warming and switch over to cleaner energy sources.

In 2009, these nations pledged $30 billion in "fast start" climate finance over the next three years, with a promise to scale that up to $100 billion per year in aid from both public and private sources by 2020.

But that latter pledge now looks increasingly unlikely — and it's one of the big sticking points at the ongoing U.N. climate negotiations in Warsaw this month.

So it's worth asking: What does this climate aid actually look like? Where has it all gone so far? And are wealthy nations really going to put up $100 billion per year in climate finance in the years to come? Here's a breakdown:

--2010-2012: The first $35 billion in climate aid. Between 2010 and 2012, the world's wealthy nations say they provided $35 billion to help poorer countries adjust to climate change, as promised at Copenhagen. (You can see a full breakdown of these pledges from the World Resources Institute here.)

The vast majority of that aid — $27 billion — came from five countries: Germany, Japan, Norway, Britain, and the United States. And most of it went toward clean energy, efficiency, and other mitigation projects around the world. Only a small slice, about $5 billion, went toward helping poor countries prepare for the actual impacts of climate change, like droughts or heat waves.

For instance, Norway gave Brazil $1 billion to help prevent deforestation. The United States gave the Congo Basin $15.7 million to preserve rain forest biodiversity. Japan gave Egypt a $338 million loan for wind power. You can see a partial list of projects in this map below from 2011 (click to enlarge):

Critics have pointed out, however, that these climate pledges didn't always add up. Oxfam International has argued that most of the aid wasn't "new and additional" — much of it was foreign aid that already existed but was simply repackaged under the auspices of climate change.

The United States, for instance, says it provided $7.5 billion in "fast start" climate finance between 2010 and 2012, spread out across more than a hundred countries. But Oxfam says that total includes existing development aid approved by Congress that the State Department says produced "climate co-benefits." It also includes loan guarantees through the Export-Import Bank that are primarily intended to benefit U.S. companies.

A recent analysis from the World Resources Institute found other twists in that initial round of climate finance. Much of the aid wasn't particularly well-targeted to climate change — there was little relationship between the recipients of climate finance and their vulnerability. That could be a consequence of the fact that most of the "climate finance" was simply aid that already existed.

--2013: Climate aid now seems to be plateauing. After the initial "fast start" round, the wealthier nations said they would help "mobilize" $100 billion per year in climate aid from public and private sources by 2020. But it's not at all clear how this will happen.

Another recent report from Oxfam estimates that global climate aid from developed countries amounted to between $7.6 billion and $16.3 billion in 2013. The report said it was impossible to get a precise estimate, thanks to "murky accounting" — those figures, for instance, likely include existing loans that will have to be paid back.

Overall, Oxfam concluded that "most developed countries are now failing to demonstrate promised increases," with the exception of Britain and Germany.

That plateau in climate finance can also be seen in these new figures from the Overseas Development Institute's Climate Funds Update, which tracks money given specifically to international climate funds — another goal of earlier talks.

As the chart on the right shows, the world's wealthiest nations have pledged $356 million to these funds in 2013, down from $1.21 billion at this point last year. (That said, nations often increase their pledges during international climate talks, so this number could go up during the ongoing U.N. climate negotiations.)

The Oxfam report says that it's difficult to see how $100 billion per year will happen by the end of the decade. Most developed countries have provided no details about their climate-finance plans for 2014, and only one country — Britain — has even said anything about 2015.

"With no clear indication of how much finance will be available in the coming years and some developed countries indicating that they have no intention to increase public climate finance over the next years," the report notes, "the $100 billion goal seems out of reach."

--Climate inequality and the U.N. talks. That brings us to this year's U.N. climate talks in Warsaw, where the unequal impacts of climate change have been a major theme — particularly after the devastation wrought by Typhoon Haiyan in the Philippines underscored the difficulty that poorer nations will have in adjusting to weather disasters that could become more likely as the world warms.

Poorer nations have pressed for more aid to help adapt, particularly since they both face greater risks but are also less responsible for the carbon-dioxide emissions currently in the atmosphere. The Philippines, for instance, is considered the third most-vulnerable nation to the future effects of global warming. Yet the nation emits just 0.9 metric tons of carbon per capita, compared with 17.6 metric tons per capita in the United States.

These discussions have been bogged down by disputes over how precisely to assign responsibility for climate damages. And there are budget constraints to contend with: Wealthier nations like the United States say that the sums of money expected by poorer countries simply aren't going to materialize. Todd Stern, the State Department’s envoy on climate issues, was blunt about this fact at a lecture in London last month.

“The fiscal reality of the United States and other developed countries is not going to allow it,” Stern said. “This is not just a matter of the recent financial crisis. It is structural, based on the huge obligations we face from aging populations and other pressing needs for infrastructure, education, health care and the like. We must and will strive to keep increasing our climate finance, but it is important that all of us see the world as it is.”

Further reading:

--A good short explanation of why poor countries are likely to be more vulnerable to climate change than wealthier ones. Basic geography plays a role. But so does poverty and weak infrastructure.

-- This World Resources Institute analysis by Taryn Fransen, Smita Nakhooda and Takeshi Kuramochi offers an excellent breakdown of the climate aid that has been pledged to date.