A comprehensive USDA study concludes rising temperatures could cost farmers millions as they battle new pests, faster weed growth and get smaller yields as climate change continues.

WASHINGTON — Climate change could have a drastic and harmful effect on U.S. [and world] agriculture, forcing farmers and ranchers to alter where they grow crops and costing them millions of dollars in additional costs to tackle weeds, pests and diseases that threaten their operations, a sweeping government report said Tuesday.

An analysis released by the Agriculture Department said that although U.S. crops and livestock have been able to adapt to changes in their surroundings for close to 150 years, the accelerating pace and intensity of global warming during the next few decades may soon be too much for the once-resilient sector to overcome.

"We're going to end up in a situation where we have a multitude of things happening that are going to negatively impact crop production," said Jerry Hatfield, a laboratory director and plant physiologist with USDA's Agricultural Research Service and lead author of the study. "In fact, we saw this in 2012 with the drought."

The National Oceanic and Atmospheric Administration said 2012 was the hottest year ever in the USA since record-keeping began in 1895, surpassing the previous high by a full degree Fahrenheit. The country was battered by the worst drought in more than 50 years, and crops withered away in bone-dry fields across the Midwest.

In the report, researchers said U.S. cropland agriculture will be fairly resistant to climate change during the next quarter-century.

Farmers will be able to minimize the impact of global warming on their crops by changing the timing of farming practices and utilizing specialized crop varieties more resilient to drought, disease and heat, among other practices, the report found. Crops also may benefit by increasing the use of irrigation when possible and shifting production areas to regions where the temperature is more conducive for better output. Depending on where they live, some farmers could benefit financially at the expense of others.

By the middle of the century and beyond, adaptation becomes more difficult and costly as plants and animals that have adapted to warming climate conditions will have to do so even more — making the productivity of crops and livestock increasingly more unpredictable. Temperature increases and more extreme swings in precipitation could lead to a drop in yield for major U.S. crops and reduce the profitability of many agriculture operations. The reason is that higher temperatures cause crops to mature more quickly, reducing the growing season and yields as a result. Faster growth could reduce grain, forage, fiber and fruit production if the plants can't get the proper level of nutrients or water.

Among the biggest threat to crops from rising temperatures and accelerated levels of carbon dioxide is an increase in the cost for the agricultural industry to control weeds, a challenge that tops more than $11 billion annually, according to the study. Warmer weather provides an ideal atmosphere for weeds to thrive, but at the same time, it can stunt the growth of traditional plants like grain and soybeans.

The entire USA is likely to warm substantially during the next 40 years, increasing 1-2 degrees Celsius over much of the country, according to the study. The warmth is likely to be more significant in much of the interior USA where temperatures are likely to increase 2-3 degrees Celsius.

The USDA review said climate change will affect livestock by throwing off an animal's optimal core body temperature, which could hurt productivity and limit the production of meat, milk or eggs. A warmer and more humid weather pattern is likely to increase the prevalence of insect and diseases, further diminishing an animal's health and output.

The 146-page report, written by a team of 56 authors from the federal government, universities, the private sector and other groups, stopped short of providing answers on how to stop or curtail global warming. The analysis was done by reviewing more than 1,400 publications that looked at the effect of climate change on U.S. agriculture.

In a separate report, the USDA looked at literature reviewing the impact of climate change on the country's forests. The data indicated the most visible and significant short-term effects on forests will be caused by fire, insects, invasive species or a mix of these occurring together.

Wildfires are likely to increase throughout the USA, causing at least a doubling of area burned by the mid-21st century. "That's the conservative end," said Dave Cleaves, a climate change adviser with the USDA's Forest Service. "We can't just stand back and let these natural conditions occur."