Climate is the average weather condition, or rather the average weather of an area, resulting from long-term observations of various meteorological elements. The climate is different from the weather, which is characterized as a natural state of the atmosphere during a short period of time. The climate defines the zones of vegetation, as well as the distribution of animals and humans on the Earth.

The distinction of the various climate varieties was made around the 5th century by the ancient Greeks. The land is divided into five zones depending on the climate:

• Equatorial or intermittent..
• Two temperate ones.
• Two polars..

This first division of Earth into zones was improved and a new division into zones of wind and rain temperatures took place. However, since the various zones do not have the same climate, a classification has been made in which the various climatic elements come together and constitute the climate types.

The type of climate is usually determined by the Köppen classification, which adopts different climate zones based on the vegetation of each region.

Tropical rainforest climate
Savanna climate
Steppe climate
Desert climate
Mediterranean type climate
Humid temperate climate
Chinese climate
Humid continental climate
Transiberian climate
Cold climate, dry during the summer months
Climate of tundra
Polar climate
Köppen-Geiger climate classification is one of the most widely used climate classification systems. The system is based on the view that the vegetation of a place determines its climate classification. The average annual and monthly temperatures and rainfall, as well as seasonal precipitation, are used to classify a climate into a category.

The climate plays a very important role, both in the plant and animal kingdom. The climate’s properties affect not only the material, but also the human moral and spiritual element, these impose the way of life, develop the spirit and generally provide the most important elements of the people’s moral and material condition. The great nations and larger civilizations developed in temperate climates, while in warm or tropical and cold climates, people progressed slowly in civilization.

The climate of some region and the Earth in general, does not remain stable. Climate variability was already known from the ancient Greeks. Aristotle characteristically mentions in his meteorology: “They are not always the same places, wet or dry, but they change…depending on how they think they should change and depending on the period...”

In modern science, we know from the scientists’ observations that there have been periods of very low temperatures in the past, the so-called ice ages. In contrast, there were times when the planet's climate was much warmer than it is today. These climate changes are something normal, but they occur over hundreds of thousands of years. The term “climate change” describes global climate change.

The climate’s paleontological changes are due exclusively to natural factors, such as solar energy, ocean currents, volcanic activity, natural-cause changes in CO2 concentrations and the shifting of the Earth's continents. In contrast, the increasing rate of our planet’s warming during the 20th and 21st centuries is not only caused by natural causes, but mainly due to greenhouse gas emissions from human activities; namely, the burning of fossil fuels for electricity generation and transport, livestock farming and the destruction of forests, oceans and other natural ecosystems.

During the 20th century, especially from 1950 and onwards, the rise of the Earth's average temperature became even more remarkable, which the scientific community directly connects with the greenhouse effect . The small amount of solar radiation that reaches the Earth's surface warms it, and the Earth in turn re-emits it as long-wave radiation (thermal radiation). The greenhouse effect concerns the absorption of a portion of the sun's thermal radiation, that is re-emitted into space from Earth, primarily from water vapor, carbon dioxide (CO2), and methane (CH4), preventing heat from escaping the troposphere into space. It should be highlighted that this phenomenon is one of the most important of the Earth's atmosphere and results in the retention of some of the infrared radiation that would otherwise be escaped. So, the average temperature on the planet's surface is at 15°C, instead of -20°C, which contributed to the evolution of life on Earth as we know it.

Although the greenhouse effect represents a natural phenomenon, the change in the composition of the atmosphere due to human activity increases the capture of the amount of heat reflected from the Earth into space and results in a further increase of the air temperature. In particular, concentrations of natural gas (water vapor 60%, carbon dioxide CO2 26%, ozone O3 8%, methane CH4, and nitrous oxide N2O 6%) increase due to human activity and especially the combustion of fossil fuels (such as coal, oil and gas). Consequently, these gases absorb thermal radiation and disrupt the Earth's energy balance and eventually the planet's climate.

Climate change, according to the reports of the Climate Change Impact Study Committee (EMEKA) of the Bank of Greece and the Academy of Athens and several other studies, affects and is expected to continue to affect the climate of Greece. The well-known temperate Mediterranean climate of our country is expected to become warmer and with less rains according to most studies.

As it emerged from the relevant analyses, the sector that is expected to be most affected by climate change in Greece is agriculture, while major consequences for the whole economy and household’s income will also have an impact on tourism and coastal systems. . The water supply sector is also of particular importance, which affects both agriculture and water supply.

Tourism in Greece is based on the climate and the natural environment, which if changed will affect the attractiveness of the tourism product. There is a strong possibility to move the tourist season towards spring and autumn due to the rise of the summer temperatures, but also water shortage. Similarly, coastal tourism will suffer from coastal erosion and the retreat of the beaches. According to the European research project PESETA, it is estimated that, in the event of an average temperature increase of 2.5 degrees Celsius, there will be a 1% reduction in overnight stays in the country, and a revenue loss of 825 million euros for the tourism industry annually. In addition, individual types of tourism will be severely hit. Ski resorts will face greater pressure, especially those at low altitudes and especially in the south. Finally, there will be very significant problems in archeological sites exposed to the data, especially those located in forest areas or on steep slopes and those vulnerable to corrosion and fires.

In terms of agriculture, Greece's climate will become drier due to the reduction of rainfalls by 20-30% during the summer and 10% during the winter. Periods without rainfall will be more, the moisture deficit will increase up to 12% and there will be an increased tendency to convert the soil to dry at 60% of arable land. The wine-producing regions that will face problems during the 20-year period 2046-2065 will be located mainly in Central and Southern Greece (because they will have the greatest reduction of rainfall and a significant increase of the humidity deficit). Also, the temperature increase can affect the quality of wine produced throughout the country, because the harvest will take place earlier.

In addition to economic and environmental impacts, climate change will also have inevitable consequences for the public health, and particularly for vulnerable groups. Those living in urban areas will face a heat wave due the temperature’s rise, which will lead to increased energy consumption for cooling.

According to the figure above, illustrating the intermediate scenario (RCP 4.5) of the projections from the University of Athens, the significant increase in temperature estimated for the summer months will certainly increase the visitor’s thermal discomfort and the inability to complete some tourist activities, therefore the level of the tourist product.

The effects of climate change are perceived in the natural environment, ecosystems and human societies. Climate change is caused by global warming, which is the observed and predicted trend for higher global average temperatures compared to pre-industrial values. Some of the effects are rising sea levels, ice melting, and changing climate zones. The foreseeable and observed negative effects of climate change are sometimes referred to as the “climate disaster”.

However, the effects of climate change are not only environmental. They are not limited to increasing the air temperature or exhibiting extreme weather events. Its consequences affect every aspect of human activity, from a country’s tourism infrastructure and agricultural production to the health of its population.

The European Environment Agency divides the effects of climate change into two categories: those relating to environmental systems and those relating to the socio-economic system and health. The first category includes impacts on the marine environment and oceans, impacts on coastal area, quantity and quality of drinking water and soil. The second category includes agriculture, forests and forestry, fisheries and aquaculture, human health impacts, energy impacts, transport and infrastructure services and tourism. The most important impacts of climate change by sector are:

• Water resources
• Coastal regions
• Fishing
• Agriculture
• Forests
• Biodiversity
• Tourism
• Built environment and transport
• Health
• Energy
• Cultural heritage

Climate change could have significant impacts on water resources around the world due to the close links between the climate and the hydrological cycle. The water cycle (also known as the hydrological cycle) is the continuous recycling of Earth's water within the hydrosphere, atmosphere, and lithosphere (soil-subsoil). The effects on the hydrological cycle are the change in rainfall distribution, the melting of snow and ice and the increase of the global sea water level.

If the drought is extended for several months, then there is talk of drought. Dryness or drought is a period of decreased rainfall (below average) in a given area, resulting in a prolonged lack of water in either its atmospheric, surface, or underground form. The drought can last for months or years and can be recorded as a drought in the short 15-day period. It can have a significant impact on the ecosystem and agriculture of the affected area, as well as tensions in the local economy.

Higher temperatures also affect water quality. Possible effects include increased eutrophication. Eutrophication is the environmental phenomenon in which excessive growth of nutrient concentration results in the reduction of dissolved oxygen in water and consequently the alteration of biodiversity in water. The result of eutrophication is the change of flora and fauna of the wetlands and the limited possibilities for recreation.

Water shortage or water scarcity is the deficiency of freshwater resources to meet the human and environmental requirements of a given area. Areas with drought often suffer from natural water scarcity. It also occurs in areas where water looks plentiful, but resources are too tied up, such as when there is overdevelopment of the infrastructure for irrigation. The fresh water available to us on the planet is about 1% of the total water on Earth. With global temperatures rising and the demand for water rising, six out of ten people are at risk of facing a water shortage by 2025. Drying wetlands worldwide, at about 67%, is one of the main reasons for this water shortage.

An equally important phenomenon is that of desertification due to water deficit and soil changes, such as condensations or waterproofing, which will become more noticeable in the coming decades. In view of the decline in rainfall combined with the increase in water demand, we conclude that the pressure of domestic water resources will increase by a large percentage.

Many infrastructures such as ports, roads and electric networks, as well as a large proportion of the industrial activities of tourism and agricultural land, are located and practiced in the coastal zone. The most important problem of the coastal zone is the high rate of coastal erosion. This erosion is set to worsen in the near future, due to the predicted rise of the average sea level, the worsening of extreme wave phenomena and the further reduction of sediment rivers due to changes in rainfall and the construction of river management works.

Η άνοδος της The rise of the surface of the sea is projected to range from 0.2 to 2 meters by 2100. In addition, other climatic phenomena that can cause coastal erosion are related to the predicted increase in wave height and the frequency of swells.

Changes in the mean sea level and meteorological intensity of wave storms (intensified by climate change) can cause extreme wave phenomena and have a correspondingly significant impact on coastal areas. Tidal phenomena can have the effect of coastal flooding, infrastructure damage, coastal erosion and the unwanted entry of salt water into lagoon, estuary, etc. habitats.

Already overfishing, pollution and disturbance of the bottom of the aquatic environment have limited fishing production. Furthermore, the impact of climate changes on the physico-chemical and biological characteristics of the water collections (rivers, lakes, lagoons, seas) is expected to have a different impact on the production potential of each water collection, as well as on its various uses.

The reduction of rainfall will affect the availability of water especially during periods of prolonged drought. This will result in a deterioration of the environment for fish fauna and a possible reduction in the production capacity of internal water collections. The increase in temperature also leads to a rise in sea level, a change in biodiversity, the structure of fishing grounds, in the sense of the biological, physical, chemical and hydrological characteristics of the seas, as well as the level of presence of the commercial value of fish. The sea level will reduce the wetlands where many fish species reproduce and live in their early stages. In addition, the temperature rise affects fish migrations to and from breeding and feeding areas, increasing the likelihood of invading foreign species.

Invasion of foreign species in Greece was observed, the lemon fish and the hare fish. They are fish that were in the Red Sea where the waters are warmer and as waters in Greece become warmer, they move this way. They are invasive. That means they don't have natural predators in our waters, which means they can't be eaten by a fish, so they're constantly expanding.

Agriculture, especially in developing countries, is considered to face quite severe impacts due to climate change. All the studies agree that in the coming years the region of Southern Europe and especially the Mediterranean will be vulnerable in terms of crop production, which is of great importance for Greece.

Agricultural production is inextricably linked to the climate, since the type and the quantity and quality of agricultural products produced depend to a large extent from it. Climatic variables that primarily affect crop productivity are temperature, precipitation, solar radiation (intensity and duration of exposure) and the composition of the atmosphere. Research with simulation models shows that the effects are expected to vary depending on the region and the crop.

Climate change is expected to affect the soil as well, reducing organic substance, which is the main factor of soil fertility.

An additional factor is soil degradation due to erosion and desertification. In addition, the increase in extreme climatic events is expected to cause more damage both to production and to infrastructure related to the agricultural sector.

In addition to plant production, climate change is expected to affect animal production. The increase in temperature will cause strain to animals resulting in a decrease in milk and meat production. Finally, due to climate change, it is expected to intensify attacks from enemies and diseases, while new species of pathogens and weeds will appear due to more favorable conditions. This may change the type, quantity and use of chemicals, e.g. pesticides and fertilizers in crops.

The need to determine the effects of climate change on agriculture is due to the fact that this change is expected to change food stocks globally, through the change in rainfall, the possible increase in temperature and CO2, the increase in extreme weather events, the change in the spread of enemies and crop diseases.

Forest ecosystems occupy about 65% of Greece's land area (25% forests, 40% meadows) and provide a variety of materials and services, as well as cultural and aesthetic value. Forests contribute to water production and quality, air quality and CO2 capture and storage, and provide habitat and food for a large number of organisms.

Forest ecosystems are mainly negatively affected by reduced precipitation and high temperatures, while the risk of catastrophic fires increases. If they are not adapted in time, forest ecosystems are at an increased risk of destabilizing them and, in extreme cases, collapsing them. Without further measures, by 2100 it is estimated that there will be a spatial redistribution of the country's forests, and the congestion (the shadow left on the ground by the earl of trees, when solar rays fall vertically) of the forests as a whole will decrease due to climate change.

The rise in temperature will increase the number of fires in the summer and the total burnt area, while the time between two successive fires will decrease. Forests of the southern mainland and Crete are expected to suffer more. It is not possible to make precise predictions of the increase in the number and intensity of forest fires caused by climate change, but there will certainly be significant increases in both the number and the destruction caused by each fire.

Structural changes in forests combined with extreme weather phenomena will result in an increase in surface drainage and erosion of up to 30%. The above is intended to lead to a reduction in the enrichment of groundwater carriers.

According to the Convention on Biological Diversity (Article 2, “Definitions”), “Biological Diversity” refers to the variety of living organisms of any origin, including, inter alia, terrestrial, marine and other aquatic ecosystems and ecological complexes, of which those organisms consist of a part. Also included is diversity within species, among species and among ecosystems. Greece's biodiversity is among the largest in the Mediterranean and Europe. Of great importance is the high endemism with many endemic species having a very limited spread making them very susceptible to disturbances.

Climate change is among the main direct causes of biodiversity loss, as well as changes in ecosystem services worldwide.

The endemic plants and vertebrates of the Mediterranean seem to be particularly vulnerable to climate change. Endemic species appear more vulnerable to climate change (based on the non-migration assumption) than other species, mainly due to their more limited range.

As regards to forest ecosystems in Greece, three change phenomena could be attributed to or linked to climate change: the drying of the fir, the invasion of conifers in deciduous forests and the drying of the forest pine.

From the wetland systems, many ephemeral systems are expected to disappear and many permanently shrink. Climate change is likely to significantly affect Mediterranean lakes in terms of availability and water quality. The reduction of wetlands will affect migratory bird routes, which mainly depend on the availability of suitable Mediterranean habitats for wintering and rest on their way from north to south.

Changes in the biochemical and physical properties of seawater resulting from global warming are likely to affect marine biodiversity, productivity and food grids. They can also boost the spread of disease, flourish of toxic algae, and spread of thermophilic species. The increased rate of invasions of the Greek seas could result from a synergy of different causes, including global warming, which creates the right conditions for the introduction and/or spread of a range of alien species, particularly some thermophilic lessepsian migrants.

By the end of the 21st century, the effects of climate change are expected to be the primary cause of the loss of biodiversity and related services offered on a global scale. Inaction or delay in adopting appropriate measures will lead to degradation or even loss of ecosystems, which will reduce the capacity of the overall ecosystem for carbon capture and storage, which will further exacerbate overheating.

Limiting water resources appears to have a significant impact on tourism. If there is a decrease in the available water due to the decrease of rainfall, it may not be possible to provide the necessary resources to tourists, which will lead to dissatisfaction and a great deterioration of the tourism product. In combination with the increase in temperature during the summer months, apart from the fact that the discomfort of tourists is intensified, there will be a decrease in external activities, resulting in the reduction or elimination of the infrastructure offered for them. The reduction of the average residence time of tourists is already observed in our country due to the weather conditions.

As there is a need to develop new bioclimatic infrastructure, it must be taken into account that the cost of the necessary infrastructure processing projects or the increase in maintenance costs will be passed on to the consumers, which leads to an increase in the prices of the tourism product, while at the same time reducing the corresponding income of tourists. Related costs are the education and adaptation of the tourism industry's workforce and the creation of new infrastructure, so that the tourism product can be modified.

Finally, Greece should be stressed the risk of degradation or destruction of areas of particular natural beauty due to forest fires, loss of beaches due to rising sea levels and decreasing river drainage and loss of archeological monuments due to extreme weather events.

The urban environment, buildings and infrastructure are highly vulnerable to climate change. Studies of the effects of climate change on the built environment are mainly focused on the case of urban centers. The building sector in Greece is responsible for about 1/3 of CO2 emissions and about 36% of total energy consumption.

The possible physical effects of climate change on the building sector are related on the one hand to the change in the building’s energy consumption with thermostatic control and on the other hand, to the change in the building’s internal climate conditions with no added energy. It is obvious that the temperature increase can bring about a significant reduction in the thermal needs of buildings during the winter and, at the same time, a significant increase in the energy needed for air conditioning during the summer season. At the same time, in non-air-conditioned buildings it can cause a serious deterioration of the conditions of thermal comfort during the summer season.

Urban management, roads, and infrastructure in general must take into account changes in extreme temperature and precipitation conditions. The flooding may result from extreme rainfall, which the urban sewage system cannot cope with. Thermal waves are increasing in cities due to the effect of urban heat.

As regards to transport, the direct effects of climate change can be found in three (3) categories. The first is the impact on transport infrastructure which may be due to natural disasters (floods, landslides) and the need for infrastructure reconstruction and repair or the implementation of projects to protect existing infrastructure from the phenomenon of climate change. Then, there are the consequences for the maintenance of the transport infrastructure and finally, we have the consequences of changes in the operation and reliability of the system due, for example to delays and other changes in routes and services.

As we know, climate and weather conditions have a major impact on human health. Therefore, climate change affects the health and well-being of populations. The World Health Organization's report on the effects of climate change on the health of European citizens points out that a temperature increase of one degree is expected to result in a 1% to 4% increase in mortality.

According to the World Health Organization, the effects of climate change on health can be, for example, included in the following three categories:

1. Direct impacts, usually caused by extreme weather events (e.g. heatwaves).
2. Indirect impacts caused as a consequence of environmental changes and ecological disturbances caused by climate change (e. increasing threat from diseases carried by mosquitoes or rodents).
3. Various impacts on populations affected by environmental degradation and economic problems caused by climate change (e. eating or even psychological problems).

The majority of the effects of climate change on Greek territory are associated with high temperature changes and heat waves of the summer months. Increasing the number of days above 35 °C is expected to have an impact on population discomfort in urban areas.

The consequences will also come from increasing storms, floods, drought waves and fires, which will affect water reserves, production of healthy foods and overall management of health systems.

It is not possible to assess the exact impact of climate change on food safety. Yet the food we consume every day, from its availability to its quality, is directly affected by climate change. The quantity of agricultural and animal products and their quality are threatened by climate change. At the same time, the ability of micro-organisms to survive and grow is influenced by the environment, including temperature and humidity. Many food-borne pathogens, such as Salmonella, grow well in warm, wet conditions. Food poisoning is expected to increase as elevated temperatures facilitate the growth, spread and transmission of such microorganisms.

Outbreaks of infectious diseases are expected due to flooding and extreme weather events, while at the same time they will cause a measurable impact on human health due to shifting populations as a result of the increase in sea levels and the increased incidence of extreme weather events.

Climate change affects energy production as well as its demand. As far as the Greek economy of energy systems is concerned, there is expected to be a big change in terms of demand and its seasonality. During the summer and especially during the months of July and August there is a significant increase in electricity demand, due to the use of air conditioning. As a result, it may not be possible to achieve the demand for energy during the warmest period of the year. In contrast, during winter the demand for electricity decreases up to 7% due to the increased average temperature.

The low water supply reduces hydroelectric power generation by 25% in Southern Europe. The increase in frequency and intensity of extreme weather events is likely to have adverse effects on the hydroelectric potential. Rising sea levels can cause problems for thermal power stations cooled by seawater and therefore adjacent to the sea. Also vulnerable in the High-Water Level are the oil infrastructure as well as some gas infrastructure adjacent to the sea, for supply by ship.

Extreme weather events are also expected to affect electricity transmission networks due to downtime losses and increased maintenance costs. In addition, the increased risk of fires is expected to cause problems in the distribution network. A positive impact on the energy sector is expected to be the estimated increase of incoming solar radiation, as well as the intensity of annual winds during the summer, increasing respectively the solar and wind potential in our country. However, extreme weather events may lead to an increase in the vulnerability of renewable production facilities.

Cultural heritage is the result of the human’s interaction with his natural environment. Cultural heritage is defined as a legacy of natural objects (cultural owneship-property) and intangible characteristics of a group or society, inherited from the older generations and preserved in the present while at the same time bestowed on the future to benefit future generations. The term Cultural Heritage includes tangible culture (such as buildings, monuments, landscapes, books, works of art and documents), intangible culture (such as folklore, traditions, language and knowledge) and “natural” heritage, which includes significant cultural landscapes and biodiversity.

In the coming years, extreme climatic events related to temperature changes, rainfall, soil conditions, groundwater and sea levels will affect our cultural heritage to a greater or lesser extent. Although even more scientific data are needed to accurately assess the effects of climate change, it is certain that cultural heritage will be affected by the phenomena directly related to it. Climate change undermines the integrity of mobile and immovable monuments. At the same time, it threatens the intangible heritage of communities, as it affects their social and economic activity and their lives in general.

1. Archeological sites: coastal erosion and retreat of coastal sections resulting in partial or total sinking of parts of coastal archeological sites, partial or total destruction of the coatings and stratigraphy of an archeological site by flood phenomena/landslides/heavy rainfall, partial or total destruction by fire, biochemical attack (erosion, carbonation, etc.) of materials and structures, damage to ancillary infrastructure (shelters).
2. Monuments: biochemical attack of materials (corrosion, carburization, elevated chlorides, metal oxidation, etc.), which leads to a decrease in the durability and strength of structures (intense cracks, separation of materials, etc.), increased cooling requirements depending on the use of each monument, chemical alteration of colors / mosaics / decor etc., partial or total destruction by fire / floods.
3. Historical Sets: disasters in buildings and other infrastructure, unsustainable cities/settlements, impact on tourism and the tourist season, there is a question of the safety or otherwise of the inhabitants of the historical sets, impact on the intangible heritage of the historical whole (traditional professions, customs, etc.).
4. Museum Collections: loss of records and collections, their biochemical attack, alteration of the cooling-heating requirements to maintain them adequately, needs for filtering and purification of the air for their adequate maintenance.