(Bloomberg Business) -- The California heat of the past 12months is like nothing ever seen in records going back to1895. The 12 months before that were similarly withoutprecedent. And the 12 months before that? A freakishlyhot year, too.

What's happening in California right now is shattering moderntemperature measurements—as well as tree-ring records thatstretch back more than 1,000 years. It's no longer just arecord-hot month or a record-hot year that California faces. It's astack of broken records leading to the worst droughtthat's ever beset the Golden State.

The chart below shows average temperatures for the 12months through March 31, for each year going back to 1895. Theorange line shows the trend rising roughly 0.2 degrees Fahrenheitper decade, just a bit faster than the warming trend seenworldwide.

12-Month Average Temperature(°F), April-March. (NOAA/Bloomberg)

The last 12 months were a full 4.5 degrees Fahrenheit(2.5 Celsius) above the 20th-century average. Doesn't soundlike much? When measuring average temperatures, day and night, overextended periods of time, it's extraordinary. On a planetaryscale, just 2.2 degrees Fahrenheit is whatseparates the hottest year ever recorded (2014) from thecoldest (1911).

California's drought has already withered pastures and forcedfarmers to uproot orchards and fallow farmland. It's costing thestate billions each year that it goes on. GovernorJerry Brown issued an executive order this month forthe first mandatory state-wide water restrictions in U.S. history,with $10,000-a-day penalties against water agencies that fail toreduce water use by 25%.

Evolution of an Epic Drought

(U.S. DroughtMonitor/Bloomberg)

These maps show the worsening conditions over the last fouryears. More than 44% of the state is in now “exceptionaldrought” (crimson). It’s a distinction marked by crop and pasturelosses and water shortages that fall within the top twopercentiles.

California has seen droughts before with less rainfall, but it'sthe heat that sets this one apart. Highertemperatures increase evaporation from the soil and help depletereservoirs and groundwater. The reservoirs are already almost halfempty this year, and gone is the snowpack that would normallyreplenish lakes and farmlands well into June.

The chart below shows a measure of drought known as SPEI. Ittakes into account both rainfall and heat, and again shows thestate in uncharted territory.

Hot + Dry = California's Worst Drought

StandardizedPrecipitation-Evapotranspiration Index, 48 Months Ended inFebruary. (WRCC/UI)

That's part of what makes this drought so troubling. The4.5 degree above-normal temps that California has seen areunprecedented, but not entirely unexpected. The International Panelon Climate Change, which includes more than 1,300 scientists,forecasts global temperatures to rise anywhere from 2.5 to 10degrees Fahrenheit over the next century, depending largely on howquickly humans reduce our dependence on fossil fuels.

That means the conditions that are wreaking so muchhavoc in California today fall well within the range of whatmay be considered "normal" in the not-too-distant future. Theimpact of such warming is expected to vary dramaticallyby region. The scientists' forecast for the U.S. Southwest:increased heat and drought—and decreased water supplies andagricultural yields.

We aren't nearing the end of California's climate troubles.We're nearing the beginning.

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