**1. Climate change**

Climate change is a problem with the highest priority facing the mankind today, influencing agricultural production worldwide. According to IPCC [1], human activities are the main factor for changes that are unique over decades to millennia. Gas emissions have increased since 1950s, reach the highest level nowadays than ever. Atmospheric concentration of CO<sup>2</sup> was less than 300 ppm from the beginning of human civilization to 1900. The present level at about 400 ppm was not reached in more than 400,000 years. The period from 1983 to 2012 was the warmest 30-year period of the last 1400 years in the Northern Hemisphere. The Earth's average temperature increased for 1.4°C in twentieth century and is predicted to increase about 11.5°C in twenty-first century. With more climate disruption by human activities, average temperature is predicted to rise in twenty-first century, heat waves are going to be more frequent and last longer, as well as occurrence of unevenly distributed precipitation in many areas. Warming and acidification of oceans will continue, followed by rising sea levels due to the melting of polar ice, and additional rainfall leads to flooding. Climate change caused by humans is significantly faster than natural global climate change during the past millions of years and most plants cannot naturally adapt according to fast changes of ecosystems caused by global warming. Temperature increases of about 4°C in late twentieth century, is reducing wheat, rice, and maize global production and with increasing food demand, seriously affecting food security. The consequences of global warming on crop production became a major task for researchers in the past decades. Also, climate change affects a number of days when plants can grow, by their decreasing of 11% until 2100. Simultaneously, extreme temperatures and rainfalls, lowering of available water, and changes in soil quality are expected to make difficulties for plants to grow and survive. Nevertheless, plants will be exposed to different abiotic and biotic stresses at the same time and their responses will be more complex with overlapping of different stress response pathways.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
