Variation in the pattern of weather, oceans, land topography and ice sheets happens overtime scales of decade or longer than that is termed as climate change. Weather is the state of atmospheric temperature, pressure, humidity and rain fall from hours to weeks, triggered by land surfaces, ice sheets and oceans combine with atmosphere is called climate system [1-3]. Climate change is a change in the statistical properties of the climate system that persists for several decades or longer, usually at least 30 years. These statistical properties include averages, variability and extremes. Climate change may be due to natural processes, such as changes in the Sun’s radiation, volcanoes or internal variability in the climate system, or due to human influences such as changes in the composition of the atmosphere or land use .
Weather can be forecast with considerable skill up to about a week in advance. Temporary changes in the climate, such as droughts, can be predicted with limited skill from season to season [5, 6]. In contrast, changes in the long-term statistics of the climate can be forecasted if caused in long duration of time, influences that are known or predictable. Climate change can be determined by many factors that influence chain of energy through the climate system, including GHGs Energy from the Sun is the ultimate driver of climate on the planet. Energy received by earth from the sun is directly dependent on the emission of energy and distance between earth and sun. Rays of the sunlight is reflected directly back to space by the atmosphere, clouds, land, ice and water surfaces. Tiny particles in the atmosphere, some coming from human activities, can increase the reflection rate of sunlight [7, 8].
Finally the solar energy trapped by Earth is returned to space as infrared radiation. In the process it strikes with the whole climate system; atmosphere, oceans, land surfaces and ice sheets. The flow of radiation in the atmosphere is very important in finding climate. The key gases that make up the atmosphere is; nitrogen and oxygen, do not interact with radiation. However, some gases are in smaller ratios absorb infrared radiation emitting from Earth’s surface and re-radiate it in all directions, including back downwards. In this way they increasing the outward flow of energy radiations to space. This is called the ‘greenhouse effect’, and the gases that cause it by interacting with infrared radiation are GHGs. The main contributors are water vapors, carbon dioxide (CO2) and methane. The greenhouse effect was came into understanding more than a century ago [9, 10]; Earth’s surface would be about 33C cooler without it, so it provides possible life temperature which keeps Earth suitable for life expectancy. \nCauses for climate change are anthropogenic as will as natural; Global climate varies naturally with time from decades to thousands of years and more. This natural fluctuation can originate in two ways: from internal variations that is energy transition, H2O and CO2 between the atmosphere, oceans, land and ice, and from external influences on the climate system, including differences in the energy gained from the sun and the effects of volcanic activities. Human behaviors also trigger climate by changing concentrations of CO2 and other GHGs in the atmosphere.
2. How Climate Changed:
Past climate has varied considerably in a manner of time scales Earth’s climate has changed dramatically several times since the earth was formed 4.5 billion years ago [15, 16]. These changes have been triggered by the changing alignments of continents and oceans [17, 18], variation in the Sun’s ray’s intensity , variations in the elliptical path (orbit) of Earth [20–22], and volcanic events . Natural variations in the concentrations of GHGs [24–26], the evolution of life  and impact of meteorite  have also caused climate change in the past. Million of years ago, for example, the average temperature of the glob was some degrees more than today and warm, tropical waters reached much farther from the equator, resulting in very different patterns of ocean and atmospheric circulation from today [29, 30]. In the past million years ago, Earth’s mean surface temperature has risen and fallen by
about 5˚C in ice-age cycles, approximately every 100,000 years or soon [31–34]. In the coolest time of the last ice age, nearly 20,000 years befor, sea level was about 120 meters below than present time [35, 36] because more water were frozen up on land in ice sheets. In the last 8,000 years, which is mostly composed of humans recorded history, have been relatively stable at the warmer end of this temperature range [37, 38]. This rhythm of stability enabled agriculture, permanent placement and population growth .
Changes in the past occurred very gradually and in a very time consuming manner, but some evidences of fast changes are also present on regional scales. For example, in the last ice age, temperatures in the North Atlantic region changed by 5°C over as little as a few tens of years [40, 41], likely due to the abrupt collapses of Northern polar ice sheets or changes in ocean currents [42–44]. Previous records shows that globally climate is sensitive to minor but persistent influences Ice-age cycles were started by small changes in the rotational motion of the Earth around the sun. These changed the seasonal and equatorial distribution of solar radiations reaching to Earth’s surface [21, 22].
Average temperature of the globe has been increased over the recent past century, while the average temperature relatively remains constant since last one thousand years till nineteenth century with a little bit variations [45, 49]. However, earth near surface air temperature rose by about 0.8C in between 1850 and 2012 [46, 50]. The rate of temperature increase since mid 1970’s and the recent past few decades is more than all that of 1850’s . The recent past decade is the warmest from all the previous ones. Satellite readings and direct measurements also show increase in temperature in the lower atmosphere over the past three decades . In contrast, the atmosphere above 15 km elevation (the stratosphere) has cooled over this time [51–53]. Temperature of the aqua’s system has also risen. More than 90% of the total heat has been trapped by oceans between 1971 and 2010 [54, 55]. The greatest increase in temperature of ocean has taken place close to the surface, with the upper 75 meter of the ocean warming by an average of 0.11C in each decade between 1971 and 2010.
3. Human activities causing climate change:
Anthropogenic activities have increased GHG’s concentrations in the atmosphere; Atmospheric level of carbon dioxide (CO2), methane and nitrous oxide started to rise around 200 years ago, after changing little since the end of the last ice age 1000 of years ago. The concentration level of carbon dioxide (CO2) has been increased from 280 ppm before 1800, to 396 ppm in 2013 [57,58]. This history of GHG’s concentrations has been derived by a combination of recent measurements [57–59] and analysis of ancient air bubbles in polar ice [47, 60]. CO2 is of prime important. Considerable amounts of CO2 are constantly exchanged between the atmosphere, land and oceans, as land and aquatic plants grow, die and decay, and as carbon-rich waters circulate in the ocean. For many thousands of years until around 200 years ago, this ‘carbon cycle’ was about in balance and steady state. The equilibrium state has been disturbed by the anthropogenic high rate of CO2 emission since 19th century, increasing CO2 concentration in the atmosphere faster than it can be absorbed by the terrestrial biosphere and the oceans community. Acidity of the oceans has been increased and increasing, the value taken out from the readings of the past 50 years shows that about 25% of average CO2 has been absorbed by oceans  and 30% by land, plant growth is also stimulated by increase in atmospheric CO2, increased nutrient availability, and responses to warming and rainfall changes (though the mix of these mechanisms remains unclear) [62–64]. The remaining 45% of emissions mix up and accumulated in the atmosphere [65–67]. Changes to the carbon cycle are understood from the measurement of the carbon value from the atmosphere [68–74], on land and in the ocean [75–78], and from modeling studies [62–64]. The main factor in the CO2 level increased in the atmosphere is the increment in burning of fossil fuels .
4. How do we expect climate to evolve in the future:
Due to the excessive emission of CO2, high level warming is anticipating, If the society remain in such a way that it is currently dependent on fossil flues, then carbon dioxide (CO2) concentrations in the atmosphere are expected to double from pre-industrial values by about 2050, and will be tri fold up to 2100 . This ‘high level of emissions’ chain for CO2, coupled with rises in the other GHG’s, is anticipated that global average temperature is going to rise by 4.5˚C up to 2100, but possibly as low as 3˚C or as high as 6˚C . A ‘low level of emissions’ chain, based on a fast shift away from fossil fuel use over the next few decades, would see warming significantly reduced later this century and beyond. It is expected that in the next several decades, global warming is going to increase the atmospheric moisture content, more intensive heat waves, fewer frosts, depletion in the thickness of sea ice, mitigation in the mountainous ice sheets and glacier, shifts in rainfall system (increases in most tropical and high-latitude regions and decreases in many subtropical and mid-latitude regions), further increase in ocean temperature, and expected rises in sea levels . The level of the anticipated change is directly dependent on the future emissions and climate feedbacks.
5. How are extreme events changing:
Climate change due to anthropogenic activities is superimposed on natural variability; due to the increase in temperature extremely cold days occur less often and very hot days occur more often; These changes are already observed [80, 81]. For example, in the recent few decades, hot days and nights are become more frequent, more extreme and longer in tandem with relative decreases in cold days and nights in many regions of the globe [80–82]. Extremes are expected to change in the future, As Climate is going to warmer because of the unending emission of GHG’s, extremes will become warmer and cold extremes will become less cold . In most of the contents of the world, a hotter extreme event is anticipated once in 20 years; at the end of the 21st century is likely to be over 4C hotter than the present. Furthermore, what we understand as a one in 20 year temperature today will become an annual or one in two year event by the end of the 21st century in most of the regions . Future changes in other extreme weather events are of lower certainty. Evidences shows that there would be fewer tropical cyclones, but that the strongest cyclones will produce heavier rainfall than they do currently [82, 87].
6. How are sea levels changing:
In past warmer climates, 129,000 to 116,000 years ago in the last interglacial period Sea level was more higher than today’s sea level that of 5-10 meters [16, 86, 87]; when world mean surface temperatures were lower than 2°C above their values just before the initiation of the commercial era in the 19th century . The estimated contributions from ocean thermal expansion  and a thin smaller Greenland Ice Sheet  imply a contribution also from Antarctica to this higher sea level.
Worldwide, sea surface are rising for 2000 years before the mid of 19th century; the long term global sea level change was lower, that was only a few centimeters per century [90–92]. Till that time, the rate of rise has increased heavily ; during 1900 and 2012, average sea level rise of about 19 centimeters are recorded [94–97]. During the previous 20 years, both satellite and coastal sea level data shows that sea level has been roused up to 3 cm per decade. A similarly high rate was observed in the 1920 to 1950 period [94, 95, and 97].
The main cause for sea level rise from 19th century till is mostly; because of sea water expansion due to the increased temperature and also due to the high influx of water due to the increased depletion rate of glaciers [98–100]. Since 1990, there have been more contributions from melting of the Greenland ice sheet, and the increased depletion of ice into the ocean from both the Greenland and Antarctic ice sheets . This increment in ice sheet discharge is directly proportional to increase in ocean temperatures adjacent to and underneath the glacier tongues and floating ice shelves that fringe the coast of Greenland and Antarctica . The combination of storage of water in land reservoirs  and the discharge of ground water [103, 104] have made a little contribution to sea level rise during the 20th century [104, 105].
7. Impacts of climate change:
Societies and ecosystem have always affected by climate change, we know from the past both natural environment and human societies both are affected by climate change. History shows various examples of societal collapse related with large scale changes in climate, ranging from the decline of the Maya in Mexico (linked to drought)  to the vanishing of the Viking community from Greenland in the 15th century (linked to decreasing temperatures) . Some of these regional climate changes took place very rapidly, on timescales similar to present rates of global climate change.
Impacts of anthropogenic climate change are already occurring; the prominent recent impacts of climate change in the natural environment are associated with increasing temperatures and increases in the number, duration and severity of heat waves [78,108]. These impacts are composed of changes in the growth and distribution of plants, animals and insects [77, 109– 111]; movement of oceanic species toward poles; and increases in coral bleaching on the Great Barrier Reef  and Western Australian reefs [113, 114 ]. few of these changes can directly trigger human activities; for example, through the effects of changing distributions of fish and other aquatic organisms on industrial and recreational fisheries , and the impacts of coral bleaching on tourism . It is anticipating that Current changes are going to continue will become more sever in the in future time, and sea level rise are expected in many areas, from the natural environment to food security and from human health to infrastructure.
Ecosystems among Australia’s terrestrial ecosystems, some of them are most vulnerable to climate change are (1) alpine systems as habitats shift to higher elevations (higher altitude areas) (2) Tropical and subtropical rainforests due to warming temperatures (moderated or intensified by rainfall changes). (3) Coastal territories are affected by sea level rise and saline intrusion. (4) In land ecosystems rely on freshwater and subsurface water that are affected by changed rainfall patterns. (5) Tropical savannahs are affected by changes in the intensity and amplitude of bushfires. Climate warming induces migration of land and ocean life away from areas that have become warmer, and towards areas that previously were too cool . Climate change also effected and affecting the food security, infrastructure and health of all living organism considerably. Climate changes have an impact on all walks of life in a chain manner directly and indirectly.
There are many factors, which are like an obstruction in the path way of accurate prediction of climate change, and many of these will persist, while advancement are needed in our understanding of climate physics and the response of the climate system to increases in GHG’s, several uncertainties are likely to persist. The rate of future global warming depends on future emissions of greenhouse gases, feedback procedures that dampen or reinforce disturbances to the climate system, and unpredictable natural influences on climate like volcanic activities. Unpredictable processes that will affect how fast the world temperature are increasing for a given emissions pathway are dominated by cloud formation, but also contain water vapors and ice feedbacks, ocean current changes, and natural cycles of GHG’s. Although from the observation of past climate changes largely corroborate model calculations, this is also uncertain due to inaccuracies in the data and potentially important factors about which we have no proved information.
It is very difficult to tell in detail how climate change will affect the location of an individual, especially with respect to rainfall. Even if a global change were broadly understood, its regional expression would rely on detailed changes in wind patterns, ocean circulation, plants and soils. The climate system can be triggered surprisingly: abrupt climate transitions have occurred in Earth’s history enormous time, the timing and likelihood of which cannot generally be foreseen with certainty. Despite these uncertainties, there is near unanimous agreement among climatologist that human induced global warming is reality [118–121].
9. Options to address climate change:
Options for emissions reduction centre is carbon dioxide CO2, is the dominant contributor to human induced climate change (Question 3). If the world sets a target of keeping the temperature less than 2C above preindustrial temperatures, then future cumulative CO2 emissions would need to be capped at around 30 years worth of current emissions (Question 4). Estimated carbon in reachable fossil fuel energy reservoirs are varying, but all agree that these reservoirs are at least several times bigger than the carbon cap for a 2C warming limit [124, 125]. Therefore, such a carbon cap, can only be met if a bigger portion of that reservoirs remain unused or alternatively if such a mechanism are brought through which we can control the CO2 emission. Methane, nitrous oxide, halocarbon gases and black carbon aerosols also have warming effects (Question 3), reduction in these emissions will reduce the warming rate [7, 126, 127].
However, the combined effect to warming over the longer term would be very less than that of CO2, so these mitigations alone cannot meet a goal such as a 2C warming limit. There are several ways to mitigate the emissions of CO2 and other GHG’s, it also include the shifting of energy supply away from dependence on fossil fuels to other energy source; energy efficiency in the domestic, industrial, service and transport sectors; mitigation in all these sectors through better system design; and efficient reductions in emissions of methane, nitrous oxide, halocarbon gases and black carbon particles. Uptake of all of these choices is under consideration now a days, and multiple studies predicting that these can be expanded effectively [124, 128].
Some Other choices are also available but have significant collateral effects. Mainly there are two interventions that could relax obstructions on future emissions, but with much uncertainties, risks, costs, and/or limitations. One would be to remove CO2 from combustion exhaust streams or from the air, and sequester it underground, in the deep ocean, or in trees or the soil. The sites where carbon damping is advised should be capable of sustaining it for centuries. Such carbon sequestration strategies face logistical, economic and technical challenges [123, 124].