Greece is headed for snap elections in January, after Prime Minister Antonis Samaras failed to persuade lawmakers to support his candidate for head of state. Bondholders are worried that the opposition Syriza party will win and back out of the deal Greece struck with foreign creditors. That explains the sharp rise in the yields they're demanding to hold Greek bonds—from less than 4 percent as recently as September.

Beijing Real-time Air Quality Index, Dec. 29

In December the Institute of Public & Environmental Affairs, a Beijing-based non-governmental organization, published a report on air pollution produced by publicly listed companies operating in China. It showed that 34 of 36 listed steel firms had committed air pollution violations between August and October of 2014. The good news, writes Bloomberg View columnist Adam Minter, is that "the mere existence of the data" suggests that "China, after decades of prioritizing economic growth over the environment, now seems willing to pressure and even embarrass some of its most powerful corporate citizens in order to curb pollution."

Barrels in the U.S. stock of crude oil in the week ended Dec. 19, excluding the Strategic Petroleum Reserve

While drivers focus on the pump price of gasoline, market insiders pay attention to how much crude oil is accumulating in tank farms. The logic? Stocks rise when supply exceeds demand. That's a sign that prices need to fall even more to encourage consumption and suppress output. The 387.2 million barrels in stock on Dec. 19 was the most for that time of year since the EIA began publishing records in 1982. That sets up the market for possibly lower prices in 2015.

Rubles to the dollar, Dec. 29

The strength of the Russian currency is a sensitive indicator of investors' confidence in the Russian economy. It took only 33 rubles to buy a dollar at the beginning of 2014, but the drop in the price of oil, coupled with Western sanctions against Russia over Crimea and eastern Ukraine, cut the ruble's value in half by mid-December. Since then the currency has recovered ground and then lost some of it. No single number will be more important to Russian President Vladimir Putin in 2015 than the exchange rate of his nation's currency.

Median U.S. annual household income in November 2014

Americans' household income has begun crawling back since 2011 in what Sentier Research calls "an uneven, but generally upward trend." But it was still 2.8 percent below the level of June 2009, when the current economic recovery began, and 5.7 percent below the level of January 2000, when Sentier's series began. The research firm adjusts its numbers for inflation and seasonal factors and measures pre-tax income. The median is the midpoint of all households' incomes. Job growth and low energy prices should continue to help incomes in 2015.

U.S. military deaths in Afghanistan as of Dec. 29, 2014

The death toll in Afghanistan from the longest war in American history should stop mounting so quickly in 2015. On Dec. 29, NATO-led forces and U.S. military personnel formally ended the 13-year war. But Americans will continue to be in harm's way as Taliban and other militants step up attacks to overthrow the government. A little over 10,000 American troops will be in Afghanistan in 2015, charged with training Afghan forces and conducting some counter-terrorism operations.

Share of Americans in Gallup poll who say that "race relations/racism" is the most important problem facing the U.S. today, as of Dec. 8-11, 2014

Will 2015 bring better race relations, or worse? Deaths of two black men at the hands of police, one in Ferguson, Mo., and one in Staten Island, N.Y., heightened racial tensions in 2014. The 13 percent figure in December was up from 1 percent in November. While 9 percent of whites named race relations/racism as the nation's No. 1 problem, 22 percent of non-whites did so. Putting things in perspective, in the 1960s the overall number got as high as 52 percent.

Amount by which the average global temperature (land and ocean) in November exceeded the 20th century average

If history is any guide, 2015 is likely to be one of the hottest years for the planet on record. August, September, and October of 2014 were the hottest ever. Thanks to cool weather in North America, November broke the streak–it was tied with November 2008 for the seventh hottest November since record-keeping began.

Operating cash balance of the federal government as of Dec. 23, 2014

The American public is typically unaware of how much money the Treasury Department has in its account at the Federal Reserve Bank of New York [PDF]. But in 2015, the U.S. will bump up against the debt ceiling again as deficit spending continues—and no one wants the government to bounce its checks. Congress has suspended the debt ceiling until March 15, 2015. The government will be able to use tax receipts and intra-government payments to stave off default for at least a few months beyond that, Shai Akabas, associate director of economic policy at the Bipartisan Policy Center, told Bloomberg in November.